EXP nerfs in the current KMST Patch.

^ There's better ways to accomplish that than to make levelling up hard in a manner that looks bothersome instead of making sure there's content to explore all the way to level 250. Certainly, two wrongs do not make a right.

Precisely, having content to explore "all the way" to 250 would mean escalating that content to fit the game progress.

We have these 3 theme dungeons:
Mushroom Kingdom
Kerning Square
Chryse

Sweet content, right?
Not really.

Grinding will level you past that content so fast, that it won't be important anymore when you're level 60, 70, or 120. Because no level 70 will say "Hey, how about going to Mushroom Kingdom to explore the level 30 content?".