So why didn’t Dr Strange use the stone against Thanos? Couldn’t he have slowed time down enough to easily kill him?

And then why didn’t they just cut Thanos’ arm off when mantis was on his head?

Why did Natasha dying not cause Banner/Hulk to lose it and run off destroying things as a red hulk only to return during the fighting and ant man makes him big and he goes ape wild on the ship tearing it to pieces? Or even better, Banner goes with Natasha to retrieve the soul stone and Natasha sacrifices herself and hulk loses it and takes it out on red skull in an epic beat down.

So much potential, but they had to go and add some bad story lines / plot elements instead of a Wrestlemania type awesome conclusion that it could have been.