In Endgame, the Thanos who comes from past to present seems more powerful. He's able to tackle Iron Man (with a more advanced suit), Captain America, and Thor (with Mjonir and Stormbreaker) very easily without having the Infinity Stones.
Meanwhile in Avengers: Infinity War, Thor was able to hit Thanos and injure him badly with Stormbreaker even when Thanos had all six Infinity Stones.
Does this mean the Thanos in past was more powerful than in present?
The Avengers: Infinity War Thanos is more powerful because he collects the Infinity Stones throughout the film and in Avengers: Endgame Thanos only gets them right at the end. The difference comes in that the Endgame Thanos is a lot more ruthless than the Infinity War one. This is because his motives have changed.
Thanos: I thought by eliminating half of life, the other half would thrive. But you've shown me, that's impossible. And as long as there are those that remember what was, there will always be those that are unable to accept what can be. They will resist.
Tony: Yep. We're all kinds of stubborn.
Thanos: I'm thankful. Because now, I know what I must do. I will shred this universe down to its last atom. And then... With the stones you've collected for me, create a new one. Teeming with life, but knows not what it has lost but only what it has been given. A grateful universe.
Steve: Born out of blood.
Thanos: They'll never know it. Because you won't be alive to tell them.
Avengers: Endgame
In Infinity War though he is still trying to only take out half of all life and so isn't using full force or even trying to kill the Avengers because that goes against his whole motto of "rich and poor alike". If he started selectively killing them because they oppose him physically it mashes with what he wants.
Thanos: But at random, dispassionate, fair to rich and poor alike. They called me a madman. And what I predicted came to pass.
Avengers: Infinity War
Note though, that Thor hitting Thanos with Stormbreaker isn't because Thanos was less powerful - he had the full Infinity Gauntlet at that point - but because Thor catches him off guard.
When asked directly if Stormbreaker was more powerful than the Infinity Gauntlet, the Russos responded with the obvious: a glove capable of wiping out half the universe’s population is more powerful than Groot’s arm attached to a sharp piece of magical metal.
“Thanos didn’t know what was coming his way and if he did he would have been able to use the stones to better react to Stormbreaker,” Sciretta paraphrased.
Inverse, The Avengers' Most Powerful Weapon Still Can't Beat Thanos, Russo Bros. Say
No. He isn't. He has always been that powerful.
Thanos is just way more confident (for good reason) in Infinity War. After all, he did have the gauntlet.
If you notice, he takes off his armour right as he is aboard The Sanctuary. He does not don it ever again.
And then, we have to remember that in IW he is there for a specific mission. Thanks to the Gauntlet, he can easily subdue anyone who crosses his path. He has no real motivation to keep fighting elaborate fights.
But the past Thanos? He's a different story. He is a warrior, who is achieving his dream of balancing the universe through brute force.
We see Thanos at his peak, at his most brutal self. He has always been a formidable warrior, strong enough to take on the likes of Asgardians and Hulk-level creatures.
It's more like, we hadn't seen Thanos at his full strength and power in Infinity War.
Their powers haven’t changed at all. The reason why Thanos in Endgame was able to put up a good fight against 3 Avengers is because he had his armour on and double-blades.
