Its been taking longer to get some exchanges since the peak after COVID. I still see loads of very good inventory as do the sightings forum.
I suspect that there are a lot of factors, including people being more educated as to how to get value, people renting out their ownership rather than putting it into II and people using what they own. Owners deeding back to MVC will play a part, but I don't believe it is big enough to be causing what you see. There is also a relatively healthy resale market that counters this trend, as people buy MVC as an excellent trader in II.
Some ownerships, Hyatt, Welk, Diamond and limited Sheraton, seem to have either a permanent or fluctuating degrading of II trading power, so this motivates some owners to rent out or use rather than exchange.
If you've been used to depositing a low season studio and getting a medium or high season 2-bed then those days may be over, but if you are trading equally or aiming up a bit, I don't see any major change. That may be different depending on specifically what you are depositing and requesting.
Before you leap to the greener grass of the points system, read up all the complaints about how difficult it is to reserve what people want that way, and decide which actually suits you better.
If you own pre-2009 direct bought you should be able to enroll for free, which is worth it if you use II for a couple of weeks per year.