To be fair, how much did Rafa spend to get them up? £50m? If you are organised with transfers and have a good coach and/or keep most of your squad you tend to be ok. To the second point, yes they'd be happy to hang around.
This isn't a short play for them, much in the same way it wasn't for City. Now, the talk of going for trophies and all that total bollocks might be, but you can run a Premier League for a fairly modest investment relative to what they have. In return, they get a massive billboard in a huge league to launder their image and further push the notion that 'Saudi Arabia isn't all that bad. You can buy a beer and watch Anthony Joshua fight.'
One thing I never see said about Man City is people talking about what they've built. I don't mean in a poetic, marvel at the majesty way, I mean they've got bricks and mortar, buildings, clubs across the globe. These are all hard assets in major markets that will increase in value. It would not shock me at all if Saudi looked at the Premier League and wanted to do similar. This is where the cash is - they just agreed a new $2billion deal for 6-years of telly rights for America. There is no promise they do it, and I don't believe MBS is a football fan like the guy in charge of Man City, but the reasons for why they did this were clear.
Why Newcastle? I assume Mandy sold the dream. Could easily (and probably should have been) Palace/Fulham or someone closer to London.