I just played arena mode on a 32-man server, and it seems pretty terrible to me. Actually, I'd say that even 24 players is pushing it; I think the best matches that I played were those with fewer than 18 players. The maps simply are not big enough to support that many players; on 32-man servers I found it nearly impossible to play sniper because rockets and grenades were being spammed at every choke point. The only arena map that I think benefits from having large numbers of players is Well, because it's actually symmetrical left-to-right, meaning that each "half" of the map can effective support the same number of players.
I see absolutely nothing wrong with it. You're only sitting out for like two minutes (sometimes less), which isn't a horribly long period of time given that on normal maps the defending team sometimes has a respawn as long as 18 seconds on the final point. Did you ever play Counter-Strike? Some rounds lasted a LOT longer than.
If you're just trying to figure out how maps work, medic isn't a bad class since you can let your team lead you around the map, and it's pretty hard to be a hindrance to your team as a medic. (Even a "bad" medic is still better than having no medic at all, and the copious amount of Heavies will likely thank you for it.) The soldier is also incredibly easy to learn how to use, although rocket jumping can take awhile to master. If you're just trying to figure things out mechanically (how the engineer works, for example), you can just start a server.
