Love the game, but gotta say - is it possible to pass the first mission of the Roman campaign on Adventure mode (with Camellius)?

I've been trying for 2-3 hours to win the final battle, and there's just no way to do it lol. No matter what army I use, it's always defeated. Might have to do with the fact that your units are Lvl 1 while the enemy ones are Lvl 10+ (since Gauls can train). Also, the enemy having heroes might contribute to that too.

tbh I've not been able to find anyone online who claimed to have done the Roman campaign. Not even reviews mention it, and there are no videos.