Time travel ruined it

So.. they can now time travel whenever they want to..? Cap even goes back to his old girlfriend and lives out his life with her (while having mjolnir and his shield and ignoring all the events in every avenger movie..)

Can they not go back in time, have sex with Thanos his mom and become his daddy?

Since it does not seem to matter if you meet/touch or even fight yourself in the past, can't they just send Thor or Marvel back 500 times for the final battle?
(basicly you send thor back, let him fight for 15 minutes then he goes to the future and goes back again when the final battle starts, rince and repeat 500 times, now you got 500 Thors..)

Is there any reason for Iron man to die? They can do whatever the hell they want, so how easy is it to save him.. how easy would it be to just kill Thanos at any time, when he was a teenager, when he was a small child..there is no reason why they can't kill Thanos and collect the infinity stones.

Sry but Endgame made 0 sense, its very hard to do a time travel movie, they should not have tried this. Would be a better movie imo if the infinity stones are impossible to destroy and work like Dragon Balls.