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FrogReaver
You can also engage in those tactics with feats and multiclassing enabled, and I believe the disruption caused by combining them is greater than dealing solely with the tactical choices you describe. Yes, a standard rogue can kite, but one with CE and SS is going to be more effective (or disruptive) when doing so, for example.
A determined powergamer will find a way to play the game the way powergamers be playin', and if that means engaging in the tactics you describe, I'm fine with that. We differ in our opinions about what's harder to manage as a DM. As I see it, most combats are about HP attrition, so I view very high DPR feat/multiclass builds as more problematic. Kiting doesn't come up enough in actual play for me to stress over, and I've been DMing long enough to
expect spellcasters to make the battlefield weird with magic. Not much to do about paladins saving their smites unless the DM feels like house ruling class features, which I largely avoid. Still, I'd rather have a no feats/no MC paladin saving his smites than warlock/paladin spamming them.
A confession as an aside: I've never actually had a powergamer at one of my home tables (AL is different), at least not the way the term is being used here. Nearly all my players are strong optimizers, though. I've also never run a table without feats and multiclassing until just last night, when my players embarked on their first adventure of a new campaign that's been in the planning for months. However, this decision wasn't made to contain powergamers, so I won't be able to provide an actual play report about the effects removing feats/MC has on that player type.
Anyway, the bottom line as far as you're concerned - if I'm reading you correctly - is that removing feats/MC doesn't reduce disruption from powergamers, and may in fact increase it. Positive or negative, the imaginary average % difference in disruption is probably rather low for either of our positions given the enormous fuzzy space we're talking about. I admit to presenting the removal of feats/MC as a handy silver bullet for problematic powergamers, and that's clearly not the case. I think it
can be helpful for DMs like myself who regard major DPR disparities as problematic, but it won't address all the underlying challenges (socially and mechanically) that powergamers bring to the table.
I will maintain that it's a handy game setting for weeding out powergamers (some, not all), if it's a matter of recruiting new players.