They're heads-up pros. Ivey and many other well-known names are not heads up specialists like these competitors. They'd likely have an edge over almost any "recognizable" name player.
The $200k pool of money for an actual 'celebrated' poker player is absolutely not worth the time and effort. Hence why you get a few tiers down in terms of player skill. Still valid tests though, you can't only compare it to the top 1%
“Your favorite poker player almost surely wouldn't agree to play any of these guys for high stakes, and would lose a lot of money if they did,” Galfond added. “Each of the four would beat me decisively.”
Names like Ben Sulsky, Doug Polk, Isaac Haxton would be big favourites over your lineup.
Galfond while still playing is playing mostly Omaha