Why Infinty War Time Travel fails

First of all we don't know for a Fact if they are going to use Time Travel to fix the snap. It's the prevalent speculation/opinion that they will use time travel. I see where you are comming from with your opinions on the matter, I just don't agree with a lot of them. I can see why people loved DofP and while I liked it I never could get over a few things. As you'll see below I LOVED, Truely LOVED First Class. DoFP just was a let down compared to First Class.

Second to you it felt thin plotted, but to me I was amazed they balanced the story arcs of what 25+ characters and not just make it coherent but actually flow well. 

Third, if while watching DoFP and watching Future Mutants die you didn't think well this is going to be rectified in a few moments then I think you got caught up in the grandeur of the shots and the story causing you not to think. Those scenes were shot gloriously, but to me they were just to get the glory shot of Mutants dying. Those deaths meant nothing to me. This is compounded by the 2 timelines occurring simultaneously.

As soon as they introduced sending Wolverine back to change the past everyone that I know of knew exactly we were going to get the Happy and I hate to say this Disney Cartoon ending. All the wrongs would be righted and all the good guys would be set on the right path. Where DoFP failed for me (I can take the fact that I knew the time travel was going to give us the happy ending) was the fact that the characters of X1, X2, and X3 never felt congruent with First Class. (or even possible to turn into their future selves) First Class was supposed to be a soft reboot and the only thing that tied it to the Original was a 30 second cameo by Hugh Jackmen and Rebecca Romijn in First Class. I can kind of see Prof X and Magneto from First Class maybe growing into the men of X1, X2, and X3. (it's a stretch for me though) The lynch pin of the movie Jennifer Lawrence's Mystique and her relationship with Professor X from First Class never felt right with X1. (Maybe it was a failure of imagination on my part, but Jennifer's Mystique never felt like any scenario would turn her into Rebecca's Mystique. Even with Rebecca's Cameo it felt like First Class took place in a completely different Universe and the 2 characters just shared a name and power set.)

The movies felt cobbled together with a "wouldn't it be great if we could pull these two Era's together" gimmick. It felt forced and gimmicky. Jennifer Lawrence phoning it in DofP didn't help either. Apocalypse furthered this not just Jennifer phoning it in, but the feeling that these characters are way to far apart. I know the timeline changed, but Jean, Storm, Cyclops, Beast, and Nightcrawler further shows that gimmicky feel that these characters will never grow to be the characters we already know. And by using the same actors in the Post Script ending of DofP in the future, acting the same way they did in X2 (X3 for Beast) says that the kids in Apocalypse should grow into those Characters. There is a huge disconnect. And the gimmick of jumping decades is just blah. 

These reasons is why I find First Class to be the superior film. They handled everything deftly. Plot, Acting, Themes, Era, everything. I could've used a better actress for Emma, but Jones was serviceable. First Class is up there with X2 and X1 IMHO. 

Fourth, Marty in Back to the Future never felt like he was in real danger. Not once did I feel like he was going to truely fade into the ether of time. The only thing that held suspense was what would change now that George stood up for himself twice. 

Fifth, what Infinity War did deftly was subvert expectations in a different way. I knew going in that it was going the be the Empire Strikes Back of the MCU. I mean that just like Empire the bad guys win, no protagonist got what they wanted. In fact, I warned my family to gird themselves against it. I told them don't be surprised if this ending is sad. The subversion doesn't come from the fact they the good guys lost. It comes from the fact that the movie is framed to where Thanos is the protagonist. His is sympathetic. His plan is bat shit crazy, but if he's not a Unreliable Narrator then his actions comes from a good place. Getting the stones wasn't easy and took a toll on him. You see that he actually loved Gamora and it hurt him to his core to do what he did. He shows respect multiple times to the Avengers. When he could he spared them. As he doesn't see himself as evil. The movie is shot in a way that his journey at times looks heroic. The scene when the Avengers have Thanos subdued and are trying to get the Gauntlet off isn't shot to look like the bad guy is being defeated. It is shot and looks like a man with principles being brought down. Thanos is fighting the odds, pain and grief to do what he thinks is right. Starlord comes off as the prick. In Starlords grief he is beating a subdued character who can't fight back. You feel for Starlord, who wouldn't want to beat the fuck out of the man who killed the woman you loved, but plays out like Starlord is the villain in that scene. When Thor buries Stormbreaker into Thanos that shot doesn't look like a Villain being almost defeated. It shot to look like a Hero fighting to do what he believes is right. After it's done Thanos is rewarded with his happy ending. His contented smile expressed through grief of losing everything including his child looks like a Hero getting a well deserved rest. 

Finally, where you saw the deaths in the other movies as significant even though the time travel was going to fix it in moments, I felt that in the dusted characters. I knew Spiderman has a movie coming out after Part 4. We assume it's after the snap or at least that's my opinion. (Although it could take place before IW. I doubt it but it's a possibility. Just like my opinion of how they fix it will be Time Travel or Jumping to other Dimensions to get their Stones. Which kinda equals out to the same. Maybe they will subvert again and Avengers 4 fixes it in another way) Knowing all that still seeing Spidey begging for life at his Father Figure and Tony who has spent 2 movies trying not to see Spidey die, slowly seeing him fade just got me. The Russo's made me feel for a fucking CGI Raccoon losing his adoptive cgi tree teenage son. Seeing the crushing weight on Cap's shoulders when he realizes they lost the battle for Trillions upon Trillions of life forms with an "Oh God" was just great acting. 

I also like having the movie end there. If it were plotted differently and the Snap and the Fixing of the Snap happened in the same movie then it would feel contrived. I like that it gives us months to dig into the plot. To try and come up with different scenarios on what will happen. Giving us a break to think who will survive, who will be brought back etc.   

I think that might be the biggest difference between you and me. We are on different sides of a coin. Both of us seeing good acting, action, scenes, etc in different places. Like my Uncle told me 100's of times it's good to have different opinions. It would be a fucking wasteland of boredom if everyone agreed. (I just think if you would state your opinions as opinions more often then it would cut down on people exploding on you. Which even I have done.)