Yeah there are a whole bunch of YouTube videos but the majority of them were made during PTR, which makes it confusing for people attempting the Set Dungeons now.
In terms of Set Dungeon difficulty, I think the Delseres Set Dungeon is slightly more difficult than Firebirds Set Dungeon but the Firebirds set just requires so much more item and skill set optimisation that it wins out on overall difficulty.
In any case, the reason that so many people are attempting Firebirds in the first place is that it is simply the first set that Wizards get from straight from Haedrig's Gifts. The majority of the players also play this game casually and don't fully understand the mechanics of the set and the skills required to get the set to work for this Dungeon, so I can understand why they get so frustrated with it and hopefully the build guide can help them out.
When I first tried Firebird, I killed everything, got meteor objective but failed in objective to set enemies on fire. Then I looked at outdated video on net and found out that I'm overkilling small stuff (video was for PTR but aplies to patch). After few tries I concluded that I must not use any other fire spell beside desintegrete or I'll kill small trash mobs before they catch fire. Even without other fire spell and with wand I use, I killed them to fast... What is there not to undestand about the mechanics of this set? When you hit 3000% weapon damage you set enemy on fire, more enemies on fire increase your DPS output. Problem is that you overpower small trash mobs with usual playable setup. Tal set I did on second try with my usual farming setup, so why doesn't setup that we use for firebird work in set dungeon? Answer: wrong monsters in dungeon, HP pool to small to showcase firebird power.
Wizard set dungeons are mostly retarded (will try to do vyr next). For firebird you need to tweek your toon so much that I cannot see how that is mastering the set (that is what the set dunegon is for). You must not have damage not to kill small mobs instantly but set them on fire, then again you have problem with killing all monsters in set time. You need to have specific items to make that meteor strikes (cold amy with 400k life to get killed only by elites and not trash mobs).
Conclusion - mastering firebird set which gains damage for setting on fire is really not having damage on your toon (???) and objective is get killed but not getting killed...
Did try Delsere and was wearing Halo ring, couldn't put slow time on enemy that were under the bubble once before, and now are slowed or frozen (???)
But that is just me, maybe I'm doing everything wrong