I love Avengers endgame,though it has MAJOR flaws

It started off so well.
The team are dealing with the emotional fall out of the snap.
 The realisation that there little jaunt to the garden has failed, they cannot undo thanos' handiwork.
Fast forward 5 years later and ant man suddenly shows up having been trapped in the quantum realm.
Only hours have passed for him not years and so he theorizes the quantum realm could be used to  travel back in time to undo the snap.

A bit of a leap to honest ,but ok.

Then we have the first major clunker the next hour of the movie.We get utterly stupid rules for time travel that not only make no sense at all,but more importantly completely destroy the tension of the mission/heist.
If as hulk says you can never change the present or future by altering the past it just create an alt time line, then why on earth did they need to sneak around??
They could have levelled the 1970s shield base with iron man tech and dug the cube out of the ruins if nothing matters.The sneaking around not contaminating the time line was all pointless and tension free by there own stupid rules of time travel.Tony could have spent ten minutes beating his dads skull in and it wouldn't have made a lick of difference to his past.
Yet still they sneak around new york ,hulk trying to act monsterish ,avoiding the present time avengers etc.

A movie that doesn't even stick to its own rules is a quite annoying one.

Then we get an absolutely slam bang brilliant ending with lots of emotional highs and happy endings for some but not all.The final battle is breathtaking,including every hero from every single movie all brought to the battleground by Dr Strange.Thanos ups the stakes and no longer wants to snap half of all life in the universe away he wants to unmake everything there ever has been and start again.
So we have big stakes and a fight for literally everything in creation against the power of a determined and angry titan.If we avoid the cringe inducing scene where we get all the female avengers suddenly all together not spread out battling thanos' army all over the map then we have a perfect ending.

Except much like thor ragnorok it felt like two different films .
The time heist felt like it was dropped in from another movie ,a bad comedy
where the writer doesn't understand basic sci fi concepts at all.
and the icing on the cake was how the hell is captain America on the bench at the end if he created an alt timeline by going back and dancing with peggy ?
Shouldn't he still be in that fucking time line not the main one?

Rant over.
I do love the film despite my unhinged, crazy ,mouth frothing over it's main scifi conceit .

but I don't love it 3000