I think many appreciate this, but one should still ask why it was omitted in the first place. I'm not a programmer but it seems... very easy to do. You just link the assets to the menu. The gameplay is just a fight so no differences there. The fact it was omitted seems indicative of laziness. Scorecards as well: it seems they just didn't feel like setting it up with the new interface. I know... they had to redo it because of the cosmetic focus. But come on, guys... I think they just tested the waters to see if they could get away with cutting things: the scorecards, the ring girls, the country colored gear,...
But I'm not mad or anything. This is 2020 and almost every dev does this. Let's release 'something' and see where the biggest complaints are and fix it. This was called beta-testing, but now that doesn't exist anymore.
But yes, I like these arena's, as I like immersion and only fight in official UFC arenas during career mode, and treat any other fight as a practice fight and do it in other arena's. I literaly haven't played event/tournament because of this omission. Surprised I didn't see anyone ask for a Kumite tourney before. I didn't realise it was impossible, but then again, I don't play that mode often if at all.