I kept in contact with 5 or 6 of the candidates from my interview date (March). They all got rejected post interview. As far as I know, I am the only one from my interview date that was WL. I checked the ARCOM class of 2022 FB members to see if anyone from my group was there, and so far no one. So I don't think they WL everyone.
I think if they WL you, it means they are actually interested in giving you a seat.
There was someone that said last year they went through the entire WL to fill the class and some rejects too, so I imagine the WL cannot be that big for a class of 150-162 students. Just my 2 cents