After level 60 or so, you've unlocked all there is to unlock when it comes to levelling up, so you're destined to gain one gem every few weeks-months to eternity through levelling up.
That's why the level up rewards should be changed, to make the gem rewards proportional to level to make levelling up seem rewarding again, i.e. level 94 grants 94 gems. It may seem a little much but it's compensatory for how difficult it is to get monsters from events like the 72h challenge. Plus, levelling up only shows more P2W offers, i.e. VoltaiK for 195 gems or whatever. It'd be nicer to have reward for levelling up instead of seeing pay to win.