EzekielRaiden
Follower of the Way
Three arguments. Theoretical, practical, and empirical.Or that if someone says "5e is Mother May I," then they should also go one step further.
Theoretical: From both explicit statements from its designers, and actual in-text citations, the game is explicitly tied to a constant, everpresent DM oversight. I do not use the word "constant" and "everpresent" lightly. It borders on "divine sustainer" levels, where it seems like every game component or element of the fictional world applies or exists solely because the DM's active, affirmative intent lies behind it. Phrases like "DM empowerment" (as if DMs ever actually lost any power) were specifically used for this reason, to exalt DMs into the highest, that their word be law unto the end of the age (where "the age" should be understood to mean "whenever the DM decides a different law is what should be law.")
Practical: The rather significant lack of DM advice present in the DMG, coupled with the mediocre-at-best tools for things like encounter building or setting DCs and using skills. As was mentioned upthread, an extremely vocal chunk of the playerbase seems to lose their collective feces whenever WotC does anything that might be plausibly read as "telling people how to run," so...the book doesn't do much to tell you how to run. The uselessness of CR in particular is my go-to example, where even outright explicit fans of 5e openly admit that CR is really no better than just eyeballing things (and may in fact be worse in many cases.) Other things, like money being useless and the economy being borked even for adventuring stuff, or Champions needing an utterly ridiculous number of combats per short rest just to keep up with Battle Masters (to say nothing of something more powerful like Paladin or Bard!) are also practical examples; the game expects many things, and is noticeably weak on the tools to do it with.
Empirical: The fact that, for at the very least the first several years after 5e came out, literally every single thread where a player asked a rules question would include some variation of the disclaimer, "This depends on your DM, who may have completely rewritten every part of this." Even I gave such disclaimers! Because they were needed. Because, as I mentioned much earlier in the thread, the game is by observation one where the rules are seen as suggestions at best.
These three things demonstrate a climate where everything you do has to be given the DM rubber stamp. Hence, whatever you do, whatever you play, whatever options you consider, you are always having to keep in the back of your mind a little asterisk saying, "Unless the DM vetoes or rewrites it." For literally everything. That, to me, is when a game is clearly in "Mother-May-I" (or, as I've taken to calling it, "Red Light/Green Light") territory. And, again, MMI or RL/GL is not restricted to OSR. I gave my 3e alignment-and-paladins example above. It can also apply in cases where designers and DMs enforce draconian hyperspecialization of the rules, where every single tiny action has a specified form, signed in triplicate with DNA fingerprinting, which AIUI was Mearls' original intent with his use of the phrase, a form sometimes called "pixelb!+@#ing." More or less, the issue isn't (strictly) that the DM decides, since the problem can also occur in games that don't emphasize DM authority nearly so hard. Instead, the issue comes, I think, from micromanaging. Which is why, for me, RL/GL carries the same overall idea: it retains the sense of being beholden, of having your moves monitored and limited. Whether that monitoring or limiting comes from "DM discretion" or from over-engineered rules doesn't really matter.