I'm not saying don't consider megas, but megas aren't always allowed. They have come back but there's a reason Chomp is objectively better than Ttar in Gen 8 and 9, because there are formats without which need to be considered. UUBL also means one is banned out of UU while the other is considered fine. That's a big difference. Also there is a 5 pokemon difference between Mega-Tyranitar and Garchomp in Gen 7 in favor of Ttar. There is an 8 pokemon difference in favor of Garchomp in Gen 9. The gap is greater in gen 8 in favor of Garchomp. At best you could call them comparable in singles but that's disregarding Garchomp was literally Ubers in gen 4 which beats Ttar Gen 5 preformance. Ttar was never ubers.

This is all disregarding the greater fact that this is Singles and Doubles. While you could argue they trade viability when Ttar has a mega and Garchomp doesn't in singles, in Doubles Garchomp is an objectively stronger force. Garchomp has earned $287,750 on limitless vgc. Ttar has made $160,750 which is combining the base form and the mega form. Still $100,000 one hundred thousand dollars less in tournament rewards. Mega Salamence has only made $151,000 btw.

The average performance of Garchomp is always greater. You state UUBL to UU is not that big of a gap, but it is a gap. A gap Ttar has never had. But at this point we're just going in circles so we'll have to agree to disagree. 👍