Since when? Kizarus only claim to fame is speed while AKainus is attack power and they get argued to be Top Tiers all the fucking time.
Kaido and Big Mom both got hyped for their insane durability and being oh so tough. Not their "combat skills" or some shit.
And well, you know how Gorosei haters used to edit in five Kaidos instead of the Gorosei to push the Agenda that they were oh so much weaker than the Yonko and lacked "aura" as if that shit matters in any regard?
If you put Topman in Kaidos spot on the rooftop Luffy would be dead right now straight up. Because he is better at Kaidos main claim to fame while also being immortal as a side hax on top.
Topman as shown in the last and current chapter, is more durable than Kaido by a CONSIDERABLE margin. Luffy made Kaido dodge his attacks in base, much less Gear 5. Meanwhile a version of Luffy that by all logic should be stronger than the one Kaido fought fucks up his hand when attacking Topman in Gear 5. Not via using some sort of move to counter by the way but JUST via tanking the hit.
And perhaps worst of all, Topman is doing all of this in BEAST mode. Not Hybrid, which he will probably not even use in Egghead and instead save for the final arc!
Topman could have less skill than pre-time skip Coby he would still be a top tier if he can fuck up other top tiers just via tanking their attacks. Straight up, if a paticular stat is strong enough? That DOES make you a top tier.
You do not need to be balanced or skillfull to be called a top tier. Not that I would even agree the Gorosei are unskilled in the first place, but even if hey were who gives a fuck if they got the hax to pay the bills anyway?