All the supreme enchants in SME have insane enchantability level ranges:
Supreme Flame: 160-300
Supreme FA 1: 160-300, SFA 2: 220-360
Supreme Sharp/Smite/BoA: 120-300, with +80 per added enchant lvl (so SS 5 is 440-620)
You dont even get anywhere close to ever roll one of those enchants naturally if its not from a loot table that just drops any random book.
It would be more reasonable to get them close to the lvl 100 range.
Suggestion:
Sup Flame: 70-120
SFA1 : 70-120, SFA2: 90-140
Sup Sharp/Smite/BoA: 70-120 with +20 per level (SS5 would be 150-200)
So all of them would have a range of 50, a lvlspan of 20 and a starting min value of 70.
Compared to range of 140 or 180, lvlspan of 60 or 80 and starting values at 120 or 160.
This would still keep all of them pretty far out of the reachable range, but enchantability lvls of loot should be increased for 2.10 anyway (i suggest using RLCraft Luckified by none other than me)
https://github.com/Nischhelm/RLCraft-Luckified