Sir, I don’t meant to slight, however I can’t refrain from interjecting a remark on your statement.
Strategic choice to ... to what? When your kingdom is over 40 states, it doesn’t stand possible to cover all area against rebellions. Given the number of lords in the royal court, a player can have 6 marshals at maximum. If a player aren’t playing on easy, invasions to other territories would need at least 3-4 marshals to advance. It leaves a player with 2 to 3 marshals to reallocate them for defence purposes. Again, given the scale of empire of 40+ states that would be a Benny-Hill-like show, trying to eliminate rebels as they would be long gone by the time even the fastest marshal with light cavalry and “strategist” lvl 3 would arrive from his seat at the rear.
I foresee you might suggest, as a matter of choice, not to have wars with anyone and control your kingdom instead. Good luck defending your kingdom against spies that other kingdoms would send you while looking at your ripe empire with ulterior animosity. Or if not expanding, then what’s the point in playing the game and how do you, Sir, suggest to win? How can one build a powerful monarchy on the sub 6 land kingdom?
The idea to bring a local commander is a good idea, yet not in the current iteration, as proposed by original poster. However, I believe there could be some balancing done to make it plausible. E.g.: high upkeep cost of such a commander and his fewer troops (as they shouldn’t be as big as marshal’s); palpable cooldown on commander’s respawn if his squad snuffed it; if commander leaves the town to chase a rebel, then he should be using garrison troops to take with him, thus leaving the city vulnerable for alien marshal‘s or famous rebel’s attack on the city (which they tend to do on hard difficulty); etc.
Given enough time and willingness to find a solution for the commander’s implementation, it is possible to find more suitable options for good balancing.