I assembled a summary of the top 10 solo seasonal greater rift clears. For the legendary gem calculation, I excluded esoteric that maxes at 100 and pain enhancer.
Conclusions about the bottom of the curve
Barbarians and monks are the weakest solo clear with average clears of 122 and 124.8, respectively. Crusaders and demon hunters have the lowest average legendary gem levels at 132.6 and 131 respectively.
Conclusion about the top of the curve
The top solo greater rift clears are for wizard and then necromancer with average clears of 134 and 131.4, respectively.
Peculiarities of the data
The #1 demon hunter has only played that class for 21 hours total in season. The #10 Witch Doctor has only played that class for 13 hours in the entire season. The top 10 barbarians are most loyal to their class while witch doctors are the least in terms of playtime per class.
The data spread
If Monks and barbs were buffed by about 5 greater rifts and wizards were brought back to the pack by 3 greater rifts, then all classes would be within 4 greater rifts rather than the current spread of 12 greater rifts.
Barbarian Greater Rift (Range = 126-119, Average = 122)
Crusader Greater Rift (Range = 136-125, Average = 127.3)
Demon Hunter Greater Rift (Range = 132-125, Average = 127.6)
Monk Greater Rift (Range = 128-123, Average = 124.8)
Necromancer Greater Rift (Range= 134-130, Average = 131.4)
Witch Doctor Greater Rift (Range= 136-127, Average = 130.2)
Wizard Greater Rift (Range= 138-132, Average = 134)
Class = Barbarian
Greater Rift (Range= 126-119, Average = 122)
Paragon level (Range= 1724-4927, Average = 3063)
Total hours played in season (Range= 129-1157, Average = 648)
Hours played for class that earned ranking (Range= 68-800, Average = 422)
Ratio of class on leaderboard vs. total play time 73%
Average Legendary Gem = 139.7
Class = Crusader
Greater Rift (Range= 136-125, Average = 127.3)
Paragon level (Range= 1786-5083, Average = 2989)
Total hours played in season (Range = 248-1674, Average = 922)
Hours played for class that earned ranking (Range= 73-1271, Average = 551)
Ratio of class on leaderboard vs. total play time 61%
Average Legendary Gem = 132.6
Class = Demon Hunter
Greater Rift (Range= 132-125, Average = 127.6)
Paragon level (Range= 1820-4382, Average = 3053)
Total hours played in season (Range= 274-1714, Average = 907)
Hours played for class that earned ranking (Range= 21-1565, Average = 504.6)
Ratio of play time of class on leaderboard vs. total play time = 61%
Average Legendary Gem = 131
Class = Monk
Greater Rift (Range= 128-123, Average = 124.8)
Paragon level (Range= 1965-4185, Average = 3462)
Total hours played in season (Range= 279-1713, Average = 992)
Hours played for class that earned ranking (Range= 43-1514, Average = 475)
Ratio of play time of class on leaderboard vs. total play time = 49.5%
Average Legendary Gem = 145.9
Class = Necromancer
Greater Rift (Range= 134-130, Average = 131.4)
Paragon level (Range= 2577-4053, Average = 3417)
Total hours played in season (Range= 522-1268, Average = 859)
Hours played for class that earned ranking (Range= 296-988, Average = 535)
Ratio of play time of class on leaderboard vs. total play time = 65%
Average Legendary Gem = 146.4
Class = Witch Doctor
Greater Rift (Range= 136-127, Average = 130.2)
Paragon level (Range= 1952-4332, Average = 3579)
Total hours played in season (Range= 272-1718, Average = 1104)
Hours played for class that earned ranking (Range= 13-604, Average = 162)
Ratio of play time of class on leaderboard vs. total play time = 19%
Average Legendary Gem = 144.4
Class = Wizard
Greater Rift (Range= 138-132, Average = 134)
Paragon level (Range= 2367-4807, Average = 3733)
Total hours played in season (Range= 399-1773, Average = 1253)
Hours played for class that earned ranking (Range= 312-1443, Average = 786)
Ratio of play time of class on leaderboard vs. total play time = 66.7%
Average Legendary Gem = 140.5