I thought he was claiming on his day he was the best. Even with those rankings I find it hard to categorsie him as one of the best. Top 10 and then you have a point.Why need? There are lots of great players never to breakthrough in a "major".
Countless top players have struggled for various reasons and never returned to former heights - Duval, Spieth, Kaymer, Donald, Day, Simpson, Walker, Mahan, etc.
Also, Gooch was a top-35 player (owgr) and top-20 (PGA Tour) before LIV and then won 3 times and finished top of the rankings, so his claim to be one of the best in the world (not the best), was certainly not unreasonable at the time.