Manbearcat
Legend
First, I'll tackle #2. How would you feel if the GM could point to some rules, or use some ultra-super-duper mechanical combo that forced your character to do something you didn't want him/her to do? Thing is, IME, powergamers (re: munchkins) get some kind of satisfaction in being able to point to something or some things in a rule book that "trumps" what the DM is describing as happening. The powergamer says "No! See? Look, I have this class, this other class, this Feat chain, this weapon, and I just used this Spell. So no, the djinn is totally visible to me, and I can also attack once for free, and I get to do it again as a Bonus action if I hit him! So...nyaaa!" In short, the PG is removing the DM's choice of how to adjudicate a game by trotting out rules and such. If a DM tried to pull that all the time on a player? *shudder*
Now, with #1. Also IME, I've found that most PG's think they are 'good at the game' because they master the rules and memorize the specials...and then spend days trying to manipulate what those rules say in order to pull off some rule-mechanics monstrosity. Why? So that they can 'win' most of the time without thinking. Y'see...knowing rules and memorizing 'power-combos' doesn't make you good at the game. It makes you good at min/maxing. Take away min/maxing, and a PG is left with little to fall back on....take away min/maxing from someone who doesn't do it, and the person doesn't even notice the game play has changed.
From your posting history, you've been running games as long as I have (1984) or a bit longer.
Now don't get me wrong, I think grotesque, paradigm-distorting powergaming (eg dart-throwing Gatling guns in AD&D or 12 classed/PRC incoherent-archetype things in 3.x) is harmful to play. However, a fair bit of powergaming is pretty much natural (it is the course of survivors in all species of our world, afterall).
With those two covered...
When I read your post above, the absolutely striking thing about it is if you simply remove every case of the words "rules", "feat", "weapon", "power", "min/maxing" and replace it with "spell(s)", you have what GMs have dealt with since time immemorial with respect to spell-caster players that effectively know how to (a) manage their spell-loadout, (b) can effectively (sensibly, logically, fairly) leverage the open-ended/purple prose aspect of spell descriptions, (c) effectively deploy utility spells to utterly re-frame important conflicts/encounters and (because of this) dictate the way a GM has to prepare a dungeon or wilderness trek in the first place!