Exactly. If you select to play as a Chapter Master then you will not be playing open battles that much, instead playing mostly commando missions or as backup for imperial armies. Field battles all by yourself should be rare and really special, requiring to muster as much chapter your can and even then most probably you'll feel overwhelmed, balanced over the fact your soldiers will scorn most damage.
You play as a Imperial Guard then be ready to play field battles all the time, defend from sieges and generally play with thousands of units in a any given battle. Special assault/command missions would be rarer but not impossible, yet very difficult compared to SM players.
Chaos could be a balance of both, or even have the complete scale as you manage CSM and hordes of traitors.
Orks along Tyranids would be the most simple faction to manage. Simply attack, attack, attack. Biomatter management for the Tyranids could be fun as you manage them as the hordes of Total War or the fleet based chapters on Chapter Master.
But EVERY SINGLE MEN/FOUL XENOS MATTERS. The difference is how much each is worth. As the SM faction you would be pressed to gather/care for gene-seed, more initiates and mounting losses will hit you hard. As the IG faction you'll have and lose soldiers by the hundreds/thousands but you need to replenish them too. So requiring more regiments and reinforces to the depleted ones would be a thing too.
And so on...