I think you’re right, and half the posts are missing the point entirely. It’s better to have a good system here on OGS rather than require outside workarounds.
The current ASTs are pretty poor:
- Poor participation for bigger boards
- Poor choice of settings (esp. for bigger boards) Live+Swiss.
- Poor choice of pairings as well - Slide or slaughter pairing for example, which may be good for the knockout Blitz ones but it’s just pairing 1dans against 18kyus and the the 18kyus just resign or die everywhere.
3d vs 11kyu
4d vs 22kyu
- Not to forgot to mention these are ranked even games which are for some reason restricted in automatch and custom games… and yet here they exist.
- Don’t forget the massive issue of about half the players forgetting when the tournaments start, or that they signed up and just time out and get disqualified. For the Swiss system as well, having the next round start completely randomly is just a pain.
I actually think this is a really clever suggestion, because many 19x19 games in a row might be exhausting, although I’m sure some would do it 
Anyway I don’t know if I need to rewrite everything that has been said before
but basically the arena system allows you to drop in and out or pause whenever you want a break from games and it will try to pair you with people of your own rank initially and then your own score in the tournament.
So if you played a few games you might get some competitively matched games in the tournament, which you probably won’t get in the ASTs right now.
So I don’t think we lose anything by swapping to an arena system (or keep both?), and maybe auto-match and custom game fulfil some of the needs of matching people for competitive games, but automatch has inflexible time settings (and blitz doesn’t even count as blitz), and the custom lists can be full of weird settings with games existing just long enough for you to read them before they’re snapped up. So nothings perfect