I'm not using resource usage as an argument for an end-user to switch, the end-user usually doesn't care about technical details. That's more for people hosting servers, who are likely to care somewhat.
The message delays would effect an end-user, and they'll determine if that's too much of an inconvenience or not for themselves. I'm pointing to it as an example of a technical problem that impacts users that seems harder to fix compared to polishing the iOS XMPP app, which was what I initially put forward in my first comment.
If I was to make an argument for why someone should switch away from Matrix, I'd just point to how often encryption fails (I've had continual and significant issues with this personally) and how laggy servers can be. If that isn't effecting someone who isn't technically inclined, then they have no real reason to switch if everything is working for them.