Maybe Zmarzlik is just so far ahead of the rest? If you removed him then I'm sure Lindgren/Holder/Bewley/Lambert/etc. would share world titles between them, just like previous generations had multiple riders pushing each other.
I'd enjoy watching Zmarzlik against the top 5/8 from 20 years ago, too, in fairness. I think he'd be very competitive.
Laguta had 4 seasons to beat Zmarzlik btw, and managed it once. I don't think he was a genuine long-term challenger, he just had the season of his life. Like Chris Holder did in 2012. You can't take it away from him, but he won't go down as a true great, I also don't think he'd have won another.