I mean in terms of disk space sure it takes up a good bit. From what I can tell winsxs takes about 10 gigs of space. But the actual wow64 subsytem only takes a 1-2 hundred MBs of RAM which is nothing for giving you that much backwards compatibility.

Rosetta 2 is going away in the next Mac OS, but that’s not going to have a massive impact on anything. The biggest impact will be the installer will be half the size since it doesn’t need twice the executables. You can download an Intel or Arm specific installer of Mac OS and it’s already half the size.

why doesn’t Microsoft treat Windows in a similar vein?

Because then nobody would use Windows. People use windows because it runs all of the programs they love. If it didn’t people wouldn’t put up with their bullshit.