It's not about making stealth more useful or more necessary, but feasible. There are times when you're going to want more reaverbots to show up (Zenny/part grinding, for instance) or, you might just have an easier time fighting and keeping enemies in front of you than trying to sneak past. I imagine most people playing recklessly early in the ruins and fighting a lot until their health gets low, then things will start to get interesting. But, yeah, it's mostly about having multiple ways to play the game and having each with its benefits and caveats. Stealth leaves more reaverbots alive and less of an escape route (if you go passive) but if you fight effectively, you can whittle down their numbers to more manageable amounts.