Earlier quoted context omitted.
After ~25 years of playing this sort of game, I am increasingly sympathetic to the idea that exponential-power leveling is just a busted mechanic. There's a variety of good ways to use it, but there isn't a great way. You can lean into it, like Disgaea, which just embraces the brokenness and writes them into its mechanics. You can just sort of write a standard game, but then, in the end, the solution to all problems…
There are games where the final score is primarily based on taking as little time as possible (e.g. the Heroes of Might and Magic series, which had its debut around the same time as Diablo); this tends to keep exponential leveling mechanics in check.
I like to play my own challenges now for minimal leveling; not formal ones for speedrunning purposes, just running more often and not grabbing all the resources. Due to the exponential nature of the game, generally if I do throw in the towel and level, by definition, the best place to grind is the latest possible place. Numerically you actually aren't missing out on much by trying to speed through the game and stopping only when necessary in most games.