As I mentioned earlier, if you really want to get this fixed, reach out to the Marriott Bonvoy Lurker. He is here to help. If you don't really want to get your LTP back, then drop it and move on. Only you know how much that status meant to you. But if I were in your boat, I'd already have PMs to all 3 of the lurkers and would still be beating down Marriott's Customer service line to get this fixed. Given it was around 10-12 years or so ago that Marriott gave LTP status to all their original members from 1981/82 and they sent a letter out to all of them, I'm guessing that is how you received LTP status. I would think any of the Lurkers could help you get that verified and help get your LT status set up to what it should be. But you will need to reach out to them to get them involved to help you.

If you really want to just drop it and move on, there are a number of existing threads comparing Marriott's program with other programs that might give you some insights into strength/weaknesses of each:

https://www.flyertalk.com/forum/marr...vs-hilton.html
World of Hyatt As Alternative To SPG Platinum After Bungled Program Merger?
Marriott vs Hyatt for Long Stays
Newbie seeking help: IHG vs SPG
Switching from IHG to Marriott... does it make sense?

Personally, if IHG will give you RA status and you will be staying exclusively at ICs, then that might be the way to go if you really want elite recognition, but the problem with IHG is outside of ICs and the Ambassador program, you won't get much elite recognition at all. Hyatt may give you the best recognition, but you need to stay enough to get their top status and you need to be staying at places where Hyatt has hotels close by (they are the smallest by far of the bigger programs.) Hilton has a history of big point devaluations and can't match Marriott at the higher-end/luxury hotels, but if you are staying mostly at HGIs, then that might well be an option.

At the end of the day, everyone needs to look at what they want to get out their hotel stays and how can they maximize what their wants are. Each program has its own strengths and weaknesses. In fact, depending on what you really want, maybe dropping program loyalty completely and go with smaller/independent hotels might be your best option.