I don't really know, having only played Medieval, and that only single-player. The Total War games aren't RTS' in the traditional C+C sense of real-time battlefield resource management, beyond directing the troops you start with around the place, or calling for such reinforcements as you might have available. You don't mine things, or seek ways to create units on the spot - you get what you take with you, but in single-player that definitely depends upon your own choices.
At least 50% of the game takes place off the battlefield, and I'd be surprised if the only multiplayer options available in Rome were to challenge one another in pre-defined battle scenarios. The turn-based nature of the back-end - the global strategy end of the game -might not be ideally suited to net-play ... but on the other hand it might! - and could easily be done.
In this back-end mode, the bases you build are your countries: they define the shape and nature of your empire, as well as what resources you have available to fund and defend it. When a region is attacked, or when you go on the offensive, you take those resources into battle. So management does come into things in this regard.
Sorry if this explanation isn't particularly clear, and as I say I'm afraid I have no idea how this translates into multiplayer. All I can say is I'd be surprised if half the game was missing. What I must stress is the sheer brilliance of the battlefield tactics! When you move on from the phase of either winning by sheer numbers, or losing by plain stupidity, there is real joy to be had in planning and executing a successful strategy. Getting to grips with shih and hsing, even in the crude digital form of Medieval Total War, is something RTS fan are born to enjoy. Sadly, getting to grips with the controls of your perspective is a battle in itself ...
Why not pick up Medieval for cheap, see how you go?