Did Respawn EVER even once say that the matchmaking in casual games is trying to "sort you with player of equal skill"? I dont think so tbh. So maybe the main problem here is that people assume that something exist even though it isnt and therefore get pissed because they feel this thing that doesnt exist is broken/badly designed. The game even says "compete against similarly skilled players..." when selecting ranked mode but NOT when selecting casual. Why would they explicitly make this distinction in the description if both modes matched you with "similarly skilled players"?
I do think there is a matchmaking in casual for sure and it IS kinda "skilled based" but NOT as you guys assume it to be. Based on my experience I think the matchmaking is trying to create "fair" lobbies, based on your team composition (premades) and how you performed in your recent matches. If your performance in a match can be categorized into four levels; bad, average, well and steamroll, the matchmaking maybe works something like this:
Lobby 1 (normal): badly-to-well performing solos + badly-to-average performing duos + badly performing trios
Lobby 2 (hot): Steamrolling solos + well-to-steamrolling duos + average-to-steamrolling trios.