I ran it perfectly on a 33MHz 486 with 4mb RAM for a long time. Even Doom II with some of its heavier maps ran fine.
"Perfectly" would mean it ran at 35fps, the maximum framerate DOS Doom is capped at. In the standard Doom benchmark, a dx33 gets about half that: 18fps average in demo3 of the shareware version with the window size reduced 1 step. Demo3 runs on E1M7, which isn't the heaviest map, so heavier maps would bog the dx33 down even more.
I'm sure you found that acceptable at the time, and that you look back on it with slightly rose-tinted glasses of nostalgia, but a dx2/66 and preferably even better definitely gave you a much better experience, which was my point.
So how does that work given that most Steam games are x86/x64 and the M2 is an ARM processor? Does it emulate an x86 CPU? Isn't that slow, given that it's an entirely different architecture, or is there some kind of secret sauce?