To answer the original question in a word: yes. They have evolved a lot. The competition bikes I am most familiar from back in the day are the YZ250 and IT175/200's. Comparing those to my MXC is interesting with the YZ but not worth the effort with the IT. My KTM is in a different universe from those IT's. It is way faster on top, has more grunt on bottom plus infinitely better suspension and brakes. I would even bet a month's pay it could hang with or beat the big bore IT's.
What I find interesting is my MXC would probably also beat those old YZ's around an MX track while still being a good trail bike. Obviously I am working from memory, but my 200 feels like it hits and pulls about the same but with a wider spread of power. So with the motors on more or less equal footing, the better brakes and suspension would easily win the day. Even my ten year old MXC is light years ahead of eighties and early 90's MX bikes much less enduros.
Every time I ride that MXC it floors me how fast and light it is. It vibrates like a big bore and drinks fuel like a Hummer. But it also flat out hauls ass while sucking up everything you hit from rocks to jumps. It makes me want an EXC300 in the worst way.
KTM 640 LC4E
KTM 200 MXC