I'm dubious, there is an asymmetry to the game that means a lower level snooker player has a bigger edge over a pool player, than the reverse.
Of course I'd agree the longer the races, the bigger the edge, but even best of 3 snooker a low level snooker pro is still going to come out on top more than a low level pool pro vs a top snooker pro in race to 8 of 9-Ball (not exactly conclusive evidence as such, but we've seen the latter, but never seen the former, even in short race snooker, i.e. Q School etc.).
As for the other part of the debate, about whether a truly top tier snooker player has won a pool event:
I think we can discount Melling and Gray as they weren't top tier players
I think we have to respectfully discount the women as the woman's game isn't professional (in any meaningful sense anyway)
That for me only leaves Tony Drago, who interestingly didn't make much money from snooker, but did have a career high ranking of 10, which I think is reasonable to consider as top tier.
As a rough guide, his financials (prize money only) as per cue tracker (
https://cuetracker.net/players/tony-drago/career-total-statistics) are as follows:
Career earnings: GBP 1,127,868
Years played: 34 (1984-2018)
Average per year: GBP 33,172.59
So for me it comes down to this. If Tony Drago was a top tier snooker player, then yes a top tier player has won a Major Pool event, otherwise no, it's never been done.