In the first of two near-decade-long Rolemaster campaigns, we ended up with this solution.the 'all caster party' neatly side-steps the problem of caster dominance. Worked for my old AD&D campaign from 1984-95.
For the second campaign, we changed some rules to reduce caster potency (basically, make melee warriors as effective as a nova-ing caster).
In any fairly traditional RPG, the GM is needed to handle the backstory and to frame the PCs (and thereby the players) into challenging situations. In more traditional D&D language, this is world design and encounter design.you shouldn't expressly need a DM. You should be able to reasonably open the book and everyone mechanically plays the same game.
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A rule-set is not a story book.
Also, RPG rules will inevitably need some sort of adjudication (eg did such-and-such a bit of roleplay count as playing to a flaw so as to earn inspiration?). Someone other than the player who has an outcome at stake needs to make this call - traditionally that is the GM. And it's not a problem if at other tables the call would have been different.