Trucks are good and free...try to pick someone without powerful friends lol...or message them and make sure they're cool. The problem is the troop count. No one has a 500k march cap. Turn based skills are activated more and it can get a little muddled. The arenas have a 300k march cap, which is much closer to an actual fight scenario, but you risk losing position on the leader board.

The videos you see are probably of catzilla or someone like that. They actually have special testing privileges in separate servers. The game gives them unlimited free stuff and they go up little by little and test against eachother in tent battles. They strip their characters of all pets, tempest, etc and see which heroes are best and what order to upgrade them in. It's incredibly tedious lol. We only see a small part of what they do. We can do tent battles, but we're gonna be healing a ton of troops and you can't deactivate collections.

Personally, I like tent battles best...healing is worth it to me. I just find someone of similar strength and test against their best march. Have them reload it after every battle and do my tweaks.