I'm not sure anyone said teams are assembled "by the same skill." The target is that everyone be in the same ballpark. And no, even that standard is often not quite met. I've said forever and a day that solo queue squads are often one experienced player, one somewhat experienced player, and one inexperienced player. But the developer was still not wrong to point out that play style differences matter. Match goals matter. And honestly, I don't believe that it's uncommon at all to get a random squad where even the weakest player may be respectable, but where that player just isn't in the mood for his squadmates' aggression or Respawn's shady matchmaking. And the net result can be the appearance of a player who, as you said, "can't keep up." To be even more honest, I can tell you from my own experience that I'm ALWAYS the most experienced player on my squad, and I can also tell you that I get tired of Respawn's "strong, less strong, weak" squad make up. And that often causes ME to be the player who is holding back, and who gives the impression of being weak. I'm not weak. I'm just unwilling.
Where I'm headed with all of this is that there can be a lot going on with players that can give the impression that we all get where teams are grossly mis-matched, but that those players are often not at all what they seem. I know I'm not. Much to the consternation of my teammates.
Where you are 100% right is that it doesn't really matter why a team is mismatched. It just sucks. But there is only so much the matchmaker can do. Is it doing everything that it can do? No, I don't think it is. But I'm starting to think, especially with the changes this season, that it's doing far more than it ever did in the past.
Nevertheless, I will take this opportunity to say what I've been saying for six years: This game needs to scrap the "fast match at any cost" primary goal that it has always had. It also needs to move "skill" farther down the list of match criteria. The primary matching parameter absolutely should be play style as self-reported by players when queried by the matchmaker. They need to be asking us a lot of questions about how we play, what our match goals are, and what it is we expect out of teammates. And it needs to allow us to update that data at the beginning of every session if we so choose. Only speaking for myself here, but I would gladly have two completely inexperienced teammates IF I had some idea that they were in the match for the same reasons that I am and shared the same outlook as me as to how to achieve goals.