Without a doubt. Once they gathered and fought him im combat he was nowhere as powerful or as versatile as the ig user. Ig user can blink heroes out of existence whereas supergirl almost killed him.
She only destroyed his armored form that maintained his vast energies, Remember he came back more powerful than ever afterwards and not even the omnipotent Spectre could stop him.
The Spectre didn't kill him because he was stealing the powers off the heroes which makes him even more laughable when comparing him to the ig user who can blink the opposition out of existence. Thanos can depower himself and destroy Am with a thought.
So you admitted he could easily defeat the heroes which he couldn't defeat. The ig blinks him out of existence. You can add the Am to the abstracts who defy him and the result is still the same.
Beating 616 abstracts isn't the be all, end all, as they're merely universal in nature, while peak COIE Anti-Monitor absorbed the power of every universe he destroyed, and beat a tanked up Spectre.
They beat AM through plot devices and weakness exploitation. Adam
Warlock did the same thing to Nebula with the IG, and only didn't get the chance to do the same thing to Thanos because he couldn't hold onto the thing. In a Flash story, we saw how easily AM could've killed the heroes if not for plot devices.
Power for power, AM is waaaaaay above the abstracts of a single universe, as proven by how he defeated Spectre, a being above Galactus (And likely the other abstracts.)
They got the ig off of her because the tactic would have never worked on Thanos. The Am was beaten down. He was beaten down prior to, leeched power off the heroes, etc. He was nowhere near as impressive as the ig and Thanos or warlock with the gems was above any hero being a threat at all.
Thanos subconsciously allowed himself to be defeated after he stomped all who opposed him. Am was bitter, was a total failure, and was killed by Superman. It's not even close in terms of power, capabilities, etc. Ig rapes any Am. There's nothing he can do to harm an ig user.
Spectre didn't want to kill him so he lived because the heroes fates were tied to his own. Am would have been destroyed had he not leeched off their powers. Context.
IG wins, as stated mere heroes could fight AM, and he was apparently weak enough that absorbing their power made a huge difference. Meanwhile the only time superheroes came close to Thanos was when he purposefully wanted them to be able too.
Funny how mere heroes are what ended up defeating Magus and Nebula when they had the IG.
As for how he could win: By overpowering him?
Also, it's laughable that your biggest argument against AM is that heroes could fight him, than claim Galactus could defeat him who's made a career of being defeated by mere heroes.
Also, the heroes that fought Thanos could be defeated by a mere Cosmic Cube, which is something Galactus is well above, despite the fact that Big G often loses to... heroes.
Come to think of it, it's odd that Quanchi pushed so hard for the current version of the Anti Life Equation in that Orion with ALE vs Odin thread, yet he's assuming Thanos is using the complete, fully working Infinity Gauntlet despite the fact that the current versions of the gems are forbidden by Eternity from working in unison.