If Thanos had, instead of randomly wiping out 50% of all living things, he had instead in each species wiped out only the dumbest 50% what would the reaction of each avenger have been?
Thanos was a fucking stupid character in the MCU. The human population is currently doubling every 61 years with a growth rate of about 1.14%. Assuming similar numbers across the galaxy, he didn't do anything except cause suffering. He's a very poorly written villain.
I guess to stay on topic, they would have looked at population growth, and determined that his plan was moronic, and fought him.
I agree that Thanos is dumb, but he's well written. He's supposed to be stupidly short sighted; that's his whole deal. He experienced a problem with his own society, and invented an idiotic solution that was readily rejected (rightly) by his own people. He saw the downfall after that and said to himself that the cause was that they didn't listen to him.
When he grew powerful enough to do it, wanting nobody else to suffer the loss of their entire society like he did, forces the universe to participate in his little exercise with little to no regard for the losses people suffer, nor the long term consequences of his plan.
He has no ability to think beyond the small scope of time that encompasses his plan.
Sure, resources will be far less scarce for people in the short term, but, as you've correctly pointed out, in the long term, he's simply delaying the inevitable, which is why his statement near the end of endgame is so poignant: "I am inevitable". Then he snaps, and nothing happens because Tony stole the infinity stones, proving he's not inevitable and underneath it all, he's not thinking of the inevitable outcome of his plan (which is only delaying things at best, and is an actual war crime).
He's convinced himself so throughly that his way is the only way that he refuses to even entertain the idea that there may be other solutions, which bluntly, other solutions may have an actual effect in the long run (more than 100 years out).
He's meant to be fanatical about it being the only option and unable to be convinced otherwise. He's written perfectly for that role.
Other means of population control should be considered, but he'll have none of it. I see it as analogous to so many humans in real life that deny long term damages to the planet and to future generations because of short sighted "freedoms" or benefits that they may reap in their lifetime. A whole "fuck the distant future for immediate gains" kind of mentality; something that, quite bluntly, is the prevailing mindset of most capitalist businesses. It's all about maximizing the present and damn the consequences.
Thanos is a literary tool to describe problems we have right here and right now, on a fundamental level. People do convinced that their way is the only way that they will do immense harm to their fellow humans (and/or other living beings) just to do what they think is in the best interest of themselves and others, without considering evidence or any discourse that may prove that their way may not work out long term.
That's because they tried to make him some sort of noble villain in the movies when he was just horny for Death in the comics and wanted to impress her