Is it really though? The average user doesn't need to know about all other clients, how it all works, etc. They just "open this website, register, and you're in!"

It's not like the registration process necessarily involves typing in the server IP and port number, picking and setting up an advanced TUI client or something else.

If you're saying the user either has to put up with a shit client (friction) or go looking for other clients (friction) (and know they have to do that (friction!)) then yes it's friction.

The Lounge is open website, type name, you're in. Matrix definitely is not.

It's beneficial for the average user to know that other clients exist at the very least; it's rather common in the matrix space I'm in that someone asks "how do I do X" without clarifying which client they use, and as such the question is unanswerable (or, worse, someone may answer with info about a different client; or they use some client that noone else does and as such noone can help them).

As some specific example, it's happened a couple times that someone's using a client that doesn't support rendering spoilers as spoilered, and as such they made unspoilered replies of something that should've been spoilered (and of course many clients (incl. the Elements) don't even have a sane way to type spoilers).