While there are legitimate points that MP rewards don't scale enough to offset the difficulty, there are some myths I would like to dispel:
Myth #1 - nobody plays high MP because it's not rewarding enough
Actually, a lot of peple play high MPs for ring runs. Many people typically farm Act 2 keys at MP7 or MP8, and do the ubers at MP10. Act 3 keys aren't an issue because they appear during xp runs. Because Act 4 is so annoying, and you need the Plans only once, I do the Infernal Machine Plans always at MP10.
So, there are rewards. They're just not necesarily of the XP/MF variety. But really -- XP comes so fast now...
Myth #2 - Higher MP doesn't give you more legendaries per kill
This is totally bunk. First of all, from the technical side -- a randomly item attempts to roll a legendary first; if it fails, it tries for a 6-affix rare, then 5-affix rare, etc. This is all described in the official game guide. Note that the guaranteed rare from an elite/champion/boss kill is an extra drop and cannot be legendary -- it's a guaranteed rare.
Now, from hard numbers: I'm level 97, and I've done hundreds of A3 solo runs in every MP from 1 to 8. I can tell you without equivocation that the higher your MP, the more legendaries per kill you will get on average. At MP6, which is an "easy" setting for me, I will get at least 30 legendaries a day. I commonly have runs that have 6+ legendaries.
At MP1, which I can basically just run through, I'll get 1-2 legendaries per act 3 "mostly full clear"; the odd run will yield no legendaries. I can't recall the last MP4+ run that I did (I clear everythng but skycrown, south of bridge wp, and keep1) that didn't yield at least 1 legendary.
When I do Ubers -- which are MP10 runs that consist of 5 stacks + 3 ubers + A1 keywarden -- one of the four people in our group, sometimes two, will get a legendary.
Personally, MP4 is probably my favorite, even though MP6 is yields better drops per hour. Why? MP4 is just much less stress, particularly on Reflect + Desecrator/Molten, and especially on mobs that have built-in shielding (like Blood Clan Occultist). I don't really like to kite, and I hate dying and running back.
Myth #3 - MP1 is still the most efficient even if you have endgame gear
This is just plain not true. Once you do enough damage AND have enough survivability, the higher MPs are better. It takes me almost exactly the same time to clear any monster power between MP1 and MP4 (I have a monk with 240k unbuffed dps). MP5-MP6 take perhaps 10-20% longer, most of that difference being slightly longer shielding trash mobs and the occasional death.
Clearly, for me, MP4 is better XP / hr than MP1. However, this was not always the case.
When we are in group, MP6 goes as fast as 24-35% runspeed allows. Packs that don't shield die as quickly as trash. In a group of 4 with very good gear, MP7 and even MP8 goes really quickly. An MP 10 ring run takes less than 20 minutes (5 packs, 3 ubers 1 warden).
If your combined effective dps for a group of 4 is around 8 million or more, you will be doing a higher monster level (To check this, solo MP10 Ghom. If you can kill him in 60 seconds, you do a little more than 2 million damage per second).
I think that the rewards for higher MP could be slightly buffed, but really, it's a good system. Most people feeling that they "have" to run lower MPs for efficiency just don't have the gear to efficiently farm the higher MPs. Remember: gear is NOT just dps. Survivability is very important because dying dramatically slows down run speeds. An "end game geared character" doesn't just have high DPS; it is nearly indestructable, too.
When my character is where I want it to be -- about 350k unbuffed dps (3 million+ actual dps output), 50k life, 750 resists -- I expect I will be able to run MP7 very quickly, and snooze through MP6.
I don't think MP8-10 will hit the sweet spot in the efficiency curve, for me. But that's ok, because when I look at diabloprogress and see top-in-the-world characters at 480-500k+ unbuffed dps -- I imagine that in a group of 4 with that type of gear, the last couple of MP's will be pretty darn fast. And there has to be something to strive for, right?
1
Myth #1 - nobody plays high MP because it's not rewarding enough
Actually, a lot of peple play high MPs for ring runs. Many people typically farm Act 2 keys at MP7 or MP8, and do the ubers at MP10. Act 3 keys aren't an issue because they appear during xp runs. Because Act 4 is so annoying, and you need the Plans only once, I do the Infernal Machine Plans always at MP10.
So, there are rewards. They're just not necesarily of the XP/MF variety. But really -- XP comes so fast now...
Myth #2 - Higher MP doesn't give you more legendaries per kill
This is totally bunk. First of all, from the technical side -- a randomly item attempts to roll a legendary first; if it fails, it tries for a 6-affix rare, then 5-affix rare, etc. This is all described in the official game guide. Note that the guaranteed rare from an elite/champion/boss kill is an extra drop and cannot be legendary -- it's a guaranteed rare.
Now, from hard numbers: I'm level 97, and I've done hundreds of A3 solo runs in every MP from 1 to 8. I can tell you without equivocation that the higher your MP, the more legendaries per kill you will get on average. At MP6, which is an "easy" setting for me, I will get at least 30 legendaries a day. I commonly have runs that have 6+ legendaries.
At MP1, which I can basically just run through, I'll get 1-2 legendaries per act 3 "mostly full clear"; the odd run will yield no legendaries. I can't recall the last MP4+ run that I did (I clear everythng but skycrown, south of bridge wp, and keep1) that didn't yield at least 1 legendary.
When I do Ubers -- which are MP10 runs that consist of 5 stacks + 3 ubers + A1 keywarden -- one of the four people in our group, sometimes two, will get a legendary.
Personally, MP4 is probably my favorite, even though MP6 is yields better drops per hour. Why? MP4 is just much less stress, particularly on Reflect + Desecrator/Molten, and especially on mobs that have built-in shielding (like Blood Clan Occultist). I don't really like to kite, and I hate dying and running back.
Myth #3 - MP1 is still the most efficient even if you have endgame gear
This is just plain not true. Once you do enough damage AND have enough survivability, the higher MPs are better. It takes me almost exactly the same time to clear any monster power between MP1 and MP4 (I have a monk with 240k unbuffed dps). MP5-MP6 take perhaps 10-20% longer, most of that difference being slightly longer shielding trash mobs and the occasional death.
Clearly, for me, MP4 is better XP / hr than MP1. However, this was not always the case.
When we are in group, MP6 goes as fast as 24-35% runspeed allows. Packs that don't shield die as quickly as trash. In a group of 4 with very good gear, MP7 and even MP8 goes really quickly. An MP 10 ring run takes less than 20 minutes (5 packs, 3 ubers 1 warden).
If your combined effective dps for a group of 4 is around 8 million or more, you will be doing a higher monster level (To check this, solo MP10 Ghom. If you can kill him in 60 seconds, you do a little more than 2 million damage per second).
I think that the rewards for higher MP could be slightly buffed, but really, it's a good system. Most people feeling that they "have" to run lower MPs for efficiency just don't have the gear to efficiently farm the higher MPs. Remember: gear is NOT just dps. Survivability is very important because dying dramatically slows down run speeds. An "end game geared character" doesn't just have high DPS; it is nearly indestructable, too.
When my character is where I want it to be -- about 350k unbuffed dps (3 million+ actual dps output), 50k life, 750 resists -- I expect I will be able to run MP7 very quickly, and snooze through MP6.
I don't think MP8-10 will hit the sweet spot in the efficiency curve, for me. But that's ok, because when I look at diabloprogress and see top-in-the-world characters at 480-500k+ unbuffed dps -- I imagine that in a group of 4 with that type of gear, the last couple of MP's will be pretty darn fast. And there has to be something to strive for, right?