In my Roman campaign with the early troops I've been beating 20 unit stacks worth of them in a seasonally basic. With some Galatians and Companions mixed in. Allot of the first stacks having 3 gold chevrons worth of experience. It’s a tough fight but I've been winning. Although my Roman troops have to go back home to Italy after every couple of battles to retrain. I'm happy with them staying as they are.