The fastest way to rank up gems is to do low grifts for low gems and slowly work your way up while barely maintaining the 100% upgrade chance. People do grift 30+ on day 1 are doing it purely to get on the leaderboard, not to rank up gems. If you don't have 100% chance to upgrade the gem you want then upgrade another one that does until you get all the ones you want over rank 25.
18 +3, 21 +3, 24 +3... and now you simply get as high as you can for your 100% chance to upgrade, or keep going to 24 for your 90%, 80%, 70%...etc. 'til your gem #1 is at 25. Then repeat on Gem #2, Gem #3.
NOW work on leaderboards. This is what I plan to do, when season hits.
Why would you go all the way to 25-30 to upgrade your level 1 gem? I'm not finding GRifts as valuable, item-wise, as simply running regular Rifts.
The lvl 30 rift boss upon failure usually gives me 3-4 legendary without counting gems. One of them from the 8 i did dropped shoulders and chest of akkhan and chest of roland. Im not sure how item wise greater rifts arent good. Im opening a present box everytime the boss i fail on is dead?