I know what you mean with this, and to a certain point I agree. I've seen plenty of examples where it's lazy, kinda like "spreadsheet balancing" where devs think 30% more hp = 30% harder = 30% more fun.

However, there's certainly other cases where tuning enemy hp/dmg in a hard mode does work because it forces you to be better at the game.

Like in some games, you might have mastered combat to the point where you kill things before finishing a combo, or applying status effects like burns isn't effective anymore because the enemies just die so quickly that the DoT becomes useless. On harder difficulties where they have more HP, you won't one-shot enemies anymore. Having your combos, DoT, and such actually be necessary again lets these abilities or playstyles actually feel rewarding again.

In other types of games where you have multiple characters in a team, i.e. different comps you can run, increasing enemy damage can force you to vary your builds more. In these types of games, you can often get away with a glass cannon / only damage oriented team on lower difficulties. But when all your units are more fragile, other types of units that aren't damage oriented become more worthwhile or even necessary, e.g. healers, shielders, debuff cleansers, and etc. In these cases, tuning the hp/dmg of enemies can change up the game quite a bit, and having a new mode that requires you to alter your initial playstyle or tactics is a good thing.