What about varying the number of levels you can get based on the difference between the level of the gem and the level of the GR? For example, if I start with a clean gem and run a level 50 GR, i can get 10-15 levels on the gem. that way, veteran characters can level gems for themselves/alts easily while new players go through the process as normal.
I like that idea actually. Keep everything the same but change the chances. Currently the GR has to be 10 levels above what the gem currently is in order to get a 100% upgrade. So every five GR levels past those initial 10 grants you an additional upgrade chance (essentially 100% until you go below the 10 level gap). So If you start with a level 10 gem and do GR 50, instead of 3 chances you would get an additional 8 chances to level for a total of 11. It also wouldn't affect higher end progression because you're always below that 10 level gap anyways when you are doing gem levels to try and push your rank. Really really like this idea!