[Garoof]

"and therefore keep it out of the package manager"

That is not much like my reasoning. Taking something out of the package manager does not generally make it so that it is taken care of by the same thing that takes care of TF2 being up to date. Making Steam handle Steam updates does.

Once you have introduced Steam as a thing that handles updates for you, moving Steam updates from package manager to Steam is clearly not exactly the same issue as removing things from the package manager in general.

(I mean, it sort of is if "the package manager should handle as many things as possible" is your goal. It is not if "as few things as possible should handle package manager-like things" is your goal.)