Simple idea. Earn 1 skill point for every 100k after hitting level 21. Or maybe 50k. Just a small little thing for people who like to continue playing their favorite character. It's not that abusable since even if you manage to get 2m extra xp we're only talking about 20 SP.
C'mon! 1 SP per 100k XP isn't worth a bot...It'd still encourage players to play less amount of alts and focus one instead of more slightly more(for example when my armorer hit 21 lvl i made another one cuz i lost motivation to make armors with maxed one)
Whenever it is possible to abuse something to get better, players will go that path, even if it takes a long time (hence the botting).