My one complaint

The Vegas part first: Why wouldn't they keep him there? They had no real use for him back home. He seemed to be doing well and was happy in Vegas. And they needed him to keep their connection to Moe Greene for when they want to make their move to Nevada.

And yes it is odd to have back to back time jumps like that, but what else did we need from those time frames? Michael comes home, joins the family business and slowly taking over as his fathers successor. There is a deleted scene from right after Michael comes home, with him and Vito talking about vengeance for Sonny and Apollonia, as well as the future of the family, but ultimately its not necessary. We don't need to see the process of it happening, just let us know (like they did) that it was happening over several years.

Then we didn't need to see Michael and Kay's wedding or starting their family. Just show us how he convinced her to come back with him, and move along with the story.

i would’ve loved to see the five families war that Michael started, that would’ve been awesome

This could be a plot hole

I agree. I wonder if it would have been better to have made one movie that ends after Michael kills Solozzo and McCluskey, and then have a 2nd movie pick up a couple of years later, to cover the rest of the time period covered in the book.
There are enough deleted scenes to stretch the run time for the "first movie" if we go with this idea (and, for me, most of these scenes shouldn't have been deleted as they enhance the viewer's understanding of the story or add more depth to the characters).
The 2nd movie could maybe include the prequel parts too in order to make it a full length movie.

Or, alternatively, end the movie after the five families meeting in 1948.

Either way, I agree with the OP. The pacing just feels off. The last 40 minutes feel rushed, and at the same time make the movie too long, so it's both too much and too little.