Stamina’s problem is how easy to ignore it is.
That’s the reason ANY investment in it, is so wasteful. Because you don’t NEED to put any work into it, to keep it in good shape.
You just won’t run out of Stamina, once you hit a half-decent lvl and stats. Not with portals and waypoints there as shortcuts. Not when, even if you spend most of a fight running around, the little stops will replenish it just fine.
I recently had to run through most of both NM Great Marsh and Flayer Jungle in one go. Didn’t clear them out quite right, so I had to quickly trace back my steps. Didn’t find anything worth stopping for, so no chance for Stamina to replenish on its own either. My Zealot is lvl 61, Ancient Armor, run always on. I never paid ANY attention to Stamina’s improvement. Barely have any bonuses, by accident of course. Didn’t come even close to depleting it. Useless.
The game has a lot of significant stats and effects. How you balance those out, how much you play “by the book” (as in, following the typical strategies) and how much you don’t… Imprints your personality into the build. And there’s enough room for both. That’s fun.
For example, and I know this is pretty “by the book,” I keep rejecting items that are technically more potent than those that give me higher run speed. Because I just love that +50% that I’ve had in my Zealot for the last several levels. It works nicely into how I handle a lot of situations by just running around. Outmaneuvering monsters and their missiles or even melee attacks. Even when I often don’t even need to. Because my Zealot only very rarely suffers a hit that makes him lose more than 30% hp. And even when diving right in and staying in the thick of it, is actually the optimal deal for such a build.
My idea, to make it useful: More inventory room.
I honestly believe a huge QoL and interesting addition, would be for some stat or calculation to be able to increase your inventory space. You know, the “backpack” where loot and Charm go.
On that, since Str is not exploited enough by the system and Stamina much less so even… Maybe those could add squares to your inventory? As in, you’re not strong/sturdy enough to carry more loot? Even if this means up’ing both stats becomes tougher, to keep things balanced out.