I went over to Discovery+ when (more or less) compelled to do so when Eurosport stopped being an entity in the UK.
The UI isn’t great – but the real problem is how insultingly glitchy the Discovery+ app is on Amazon Firestick: it is utter dogshit. In my experience it will open correctly after crashing the on first attempt. Give yourself 2 minutes swearing time ahead of planning to watch anything.
The web (i.e. browser) offering works without problem (in my experience – YMMD) on Safari/Chrome/Firefox on Mac OS. I can’t speak for other platforms.
Given how much of the market the Amazon platform has (and given how no other app on that platform performs as reliably miserably) they need to up their game.
The actual content is essentially the same Eurosport offering – generally very good,