Stamina does bug me but it's more for keeping Creation's corruption level low for the best ending as Druid. Experience is not really an issues.Honestly, the stamina system still bugs the ever living shit out of me. The MC has so many options for restoring whole chunks of stamina, but all your followers can do is sit and wait for at best 26 stamina per day. I know there's other things to do besides portal runs, but I either have to run them solo most of the time which just leads to me getting my ass handed to me or juggle several dedicated portal teams just so I don't need to sit on my ass most of the game. That just ends up slowing down experience grind to an abysmal crawl honestly.
There are many ways for experience grind but I found the easiest way is to farm the king's first fight. Another way is with one or two good unit, you can drag the rest of your team level up with a few unstable portal run which gives extra experience. Finally you can take Giant Slayer and spam boss bait in a world. A mushroom or so give good xp