Yes, but I don't feel that a message app really needs to do this to the extent that Telegram does–they've managed to make their app look out of place on macOS.
The rest of the apps I find myself using don't use those same UI/UX patterns/designs, and I don't think it matters that much: Photoshop, Terminal, Telegram, Bear, Fantastical... the list goes on. The applications that keep me coming back are the ones that are smooth and don't interrupt my train of thought (most everything here), or have some big use case (Photoshop) that keeps me coming back.
I'll also point out one more time that Telegram is what people bring up every time this discussion rolls around, so they're clearly doing something right and people must not think it looks _that_ out of place.
Hell, I'd argue that the consistency of UI/UX on Apple products matters more for the initial purchase and wow-factor than it does once a user has settled into their environment. Every application does not need to function and look exactly the same.
To be honest, this all feels like moving the goalposts, and is why I usually refrain from getting into these discussions.
EDIT: Leaving aside the question of whether the other multi-platform messaging apps also do it that poorly, and merely running with your assertion to that effect. I have neither the time nor the inclination to gather data on that question.
So if you know a way to achieve your ideal, then you can propose that alternative, and you can say, here is how, without much more cost of development, you can achieve X, Y, X improvement on performance while keeping all features. But, if you do not know, and have no known examples, it could indicate that it is not currently technically known how, and thus impossible with the current hardware and software knowledge at hand.
I'd also say that in the case of Slack, their ideal is probably defined more in terms of profits. So it could be said to be the right choice, simply because of how popular their service is and has remained, even though they picked Electron for their desktop client.
Why not just use another tab in your existing browser then? Or another service entirely?
Either way, it doesn't change anything in creating a widely used application for the least amount of time and effort. The vast majority of their users will not care or even notice if there was a more efficient native app.
My employer dictates the choice of communications tool. I don't just get to "pick another service entirely."
EDIT: And their site's 2FA (which I'm required to use, because $work) also reliably gives me "too many login failures" on the first login attempt, so using it in a browser tab is a non-starter, even without also losing desktop notifications.
With the amount of money they've been given, both by VC and by customers (I know what we pay them per month, and although we're not a small company, we're far from their biggest customer), this quality of software and service is absurd.
I also pointed out Telegram because people, consistently, in every one of these threads, trot it out as an example of a native chat app (I don't count the Qt version in any of this, because it does not in any way feel native on macOS).
To be honest, I welcome anyone to point out a competing cross-platform chat application that does almost as much as Slack does and doesn't eat up memory.