Xbox

All Microsoft games will be on Gamepass, so you wouldn't have to worry about Flight Sim specifically. I did the Gold to Gamepass conversion for 3 years and have found it very worth it, but it's hard to say at retail cost if I'd still sub.

I used this trick to get three years of Game Pass for about 4000 INR. Not sure if it still works: https://www.pcworld.com/article/397667/get-3-years-xbox-game-pass-ultimate-tip.html

Generally worth it.

There are lots of games on there that I'm interested in playing but don't feel it is worth spending $20+ on. And even if there are only a few day one releases I would want to buy on there, it pretty much pays for itself.

They do rotate non first party games in and out. Usually there is a "leaving soon" notice posted. When the game is removed you can't start it any more but you save/data is still preserved. If you really want to keep playing you can buy the game and pick up where you left off. This has happened to me zero times (most games left after I was done with them).

Re: ultimate, yes and I think access to games on the PC too?

I was in the same boat when I bought the xsx. But it's worth it, and I play games from my backlog in descending order. So I play first games that have been on the service the longest. Games that I love when they leave the service I will buy, but so far that's a hand full after having the xsx for 2.5 years.

First party titles like Flight Simulator will never leave the service by the way.

Also there is the gold conversion trick. There are guides on reddit, but essentially means that you let current subscription expire, then get up to 36 months Gold (using codes) and then subscribe for 1 month to Ultimate. All Gold time will be converted 1 to 1 to Ultimate. It's very important that this only works if you've no active GPU subscription.