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When Thanos fights the Avengers in Infinity War, he always has the Power Stone because that's the first he collected. So he has been fighting with increased power, yet some of the Avengers were able to resist him.
However, in Endgame the same people are fighting him all at once, but can barely resist.
In Infinity War, Wanda was destroying the Mind Stone with one hand, while pushing Thanos back with the other hand. And she actually did destroy that Infinity Stone with one hand, so she was using so much energy on that mission and wasn't fighting back Thanos in full power. But in Endgame, even using both her hands, she is not strong enough to push him back for more than 3 or 4 seconds.
In Infinity War, Captain America, merely a human with strong muscles, can fight Thanos (who had just thrown a moon on Iron Man!) and resist against his punch for some seconds. Meanwhile, Captain Marvel uses her photon blast and superhuman strength to fight him hand-to-hand. Remember that she can carry a spaceship on top of her head all the way from nowhere in space to Earth, and can destroy spaceships just by flying really fast towards them, and doesn't get killed while doing so. Which is faaaaar more that what Steve is capable of, but Thanos throws her like an apple. Or the moon he threw on Tony.
My point is, I know Thanos is strong, he is a Titan, his skin is unbreakable, highly skilled in combat, etc. But we've seen in Infinity War that some heroes can stand against him while he has the Power Stone. Yet in Endgame, they are no match for Stone-free Thanos.
P.S. I did not ask why Thanos is strong. Read the question before marking it as duplicate, please.