First of all, it is a great game! Congrats to the whole team.
On legion battles, I feel they make the game distinct and feel natural to the environment. I do however agree that it needs work and the direction the devs are thinking on are promising. Here are some changes I feel might be worth exploring:
Optional tactical missions before battles. Outcomes affect bonuses, penalties, loot and other variables. Duel to small scale (2-10 people), multiple and/or random objectives (kill lieutenant, destroy supplies, posion water, set traps, etc.). Available for Companions and Praetorians as well as Centurions.
Optional tactical missions during battles, with similar possible outcomes, scale and objectives as preparation missions. Tiny map with fighting soldiers serving as boundaries. Only available to Centurions, accompanied by random allied soldiers.
Option to autoresolve battles.
Other systems might also benefit from a revision:
Party: the division between Praetorians and Centurions seems forced and ends feels limiting.
Auto level up: I would like to be able to create "skill templates", that we can assign to a party member so that they level up automatically getting the skills in the chosen template.
Items: very soon in the campaign items start flooding in with small but relevant different skills and stats, making outfitting the team start to feel more like a chore than an enjoyable experience pretty quickly.
Weapon actions: I like how weapon action variety open new tactical options. But given its impact on tactical missions (my most enjoyable aspect of the game), it seems excessively random and out of the player's control.
Hope some of this helps.
Cheers
