Well, it technically depends on what's in the terms and conditions. Generally speaking though, that's like saying Youtube owns any video posted rather than the channel host. Granted, that's not an excellent example, but it still shows the point very well. Even if Youtube does profiteer off the channel hosts, the channel hosts still ultimately "own" their content as far as copyright is concerned, which is why certain accounts seem to attack one another with copyright claims and strikes.

Ultimately, copyright exists so that a person's work remains that of the person and any affiliated parties, and while you can get it nice and legalized, the copyright still technically exists without a fancy piece of paper. Again, though, about affiliated parties, reading the fine print is super important in situations like this.