There is going to be no metric that makes any kind of sense to select at-large bids this season as teams are going to have vastly different numbers of games played (as an example Memphis in the AAC has played 4 games, Temple has played 0 so far). What is going to happen even more this year is mediocre P6 teams are going to fill out the bracket, because there will be zero ability to really compare, say, an ETSU with a Penn State (and let's be real, ETSU would have gotten shafted last year had they been upset by Furman or UNCG in their conference tournament, despite doing 27-4 and having an NET in the 30s). 32 teams in a year like this year with auto-bids only is really the only equitable way split the pie.
There also wouldn't be 20 cream puffs because there are good teams in those lesser conferences. What are we talking about...top 12 conferences. Last year that would have been the P6+A10, AAC, WCC, MWC, MVC, and MAC. That wouldn't have included teams like Liberty, ETSU (there were actually three Southern schools in the top 100 last year -- ETSU, Furman, UNCG), Stephen F. Austin, Louisiana Tech , Vermont, Winthrop, Yale, or Belmont. So assuming most likely these would have been your reps from outside the top 12 conferences...that's actually 20 teams that would be playing quality basketball out of 32 (so the opposite of what you said). I would assume any REAL cream puffs could be gone outside of the first round, and most of these teams would probably be gone after the round of 16 (pretty much like any year).
I get it, people want to see brands and what is equitable isn't necessarily popular. I'd also say the P6 will be just fine if this were the format for one year.
Of course, this whole conversation is moot in the sense that the Ivy League and Patriot League cancelled their entire seasons anyway, which would leave you with 30 teams.