Plenty of guys go up and win matches against good competition. I'd say Adam Satiev was undersized for 85 when he won in 2000. Dabir went from 58 to 63 and was a bad clinch call away from winning gold. Paslar won his gold the same tournament standing a foot under everyone else. The list can go on and on. Including guys going down a weight and doing worse. Hwts are at a disadvantage in this because they can't go up and beat anyone so they either beat a smaller man or lose to him, a lose-lose situation. I love Gatsalov and his hwt world championship was great to see but styles make matches and it's not like Gadisov or Sadullaev would be able to accomplish the same thing.
We should also bring up the football and basketball stealing larger athletes argument. Even though worldwide soccer is way more popular and I don't see too many potential heavies out on the pitch.
Most wrestling cultures care way more about heavies than any other weight. The Russian's are doing another hwt only tournament for a bunch of money. The only Iranian to win gold at hwt became a huge celebrity and pretty much retired after his gold. Ghasemi was the flag barer for the closing ceremonies because he medaled at hwt, despite having a few gold medalests at other weights. The Indo-Canadian community shares these feelings too having hwt only tournaments and they used to give $5,000 to the winner of the 96 vs 120 match at the Hargobind. All of this leads me to believe anyone who thought they could have success at hwt would try to.