Yea, I guess if you get the right trader or whatever, II can be great - also if a getaway works for you or whatever. But II is a lot more limited IME than RCI for finding "something". I regularly get 0 results in a search from II both with ACs, with exchanges, for getaways. Even more often there will be 2 options. With RCI, to get only 2 options I have to be extremely limited in area or picking a very specific resort to get that. If I search "All Maine" or whatever, something's going to turn up. II not so much. Not saying they'll be great, but I do see how RCI stays relevant - if you can't pull Marriott in II, there's a very small number of resorts / locations - at least where I'm looking / going. Or a small number that fit my needs (2BR or multiple 1BR concurrently).
What I do think is true is the opaqueness of II means that I can't really compare between different people easily. Whereas with RCI I can be pretty sure that if I get X points - you'd see the same things with X points.