That's an interesting question and I bet you'll get different answers based on how old (or wealthy) the user was. I'm basing my thoughts around socket 7 since you mention MMX and thinking about the average gamer, not somebody who had thousands to spend every year on a new machine. S7 was also in my mind THE system of the late 90s multimedia age, freaking everybody owned one.Real world experience doesn't match up with magazine ads from the time usually, like who in their right mind actually could afford a Coppermine P3 in late 1999 😜.
I used a Pentium 133 until the year 2000 when I was gifted an upgrade to an ss7 and k6-2 350mhz (which is what I played diablo 2 on like an addict in high school). It was very common up to the year 2000-2001 to see the average person still running a Pentium chip, or it was for me as a high school student when most of us inherited our fathers old PC while they upgraded to Pentium III or Athlon systems. Pentium 2 systems weren't too common and P3 rigs were prohibitively expensive until the 2000s.
From 2001 to 2003 consumers saw the massive clock speed explosion happen, leaving anything socket 7 right in the trash bins (literally). My ss7 rig was finally retired in late 2001 when I got an Athlon XP.
I would say late 2000 to 2001 was really the end of the useful life of an mmx for "gaming", but with the mindset I had for gaming back then where extremely low FPS meant playable. D2 ran like crap on ss7 setups but tons of us did it anyway. If you needed buttery smooth performance between 1999 and 2001, you had to spend thousands. 2001 was the point where Athlons and 370 pentium IIIs and early pentium 4s started showing up in the average home.
Sup. I like computers. Are you a computer?