Yes, that's why you need independently developed and independently distributed client software. Otherwise there's no meaningful compartmentalization.

The parent poster is not rejecting end-to-end crypto itself, but how it's typically done. (on a locked phone you don't really control in an autoupdating app you don't control at all) Web based end to end encryption is even more ridiculous (say mega.nz for example), because then it's even more trivial to distribute different code to differnet users.