On Android... Slow and laggy: not in the least, maybe this is IOS specific. Giant text bubbles: again on Android this is not a problem. Dark mode: Signal has had this for well over a year at this point. GIF support on Android has been there for almost a year as well.

The downside to Telegram? I don't trust it - so even if any of the above we're true they're all subjective and in my mind not worth compromise.