I don't think the demi spires actualy have resistance at them yet. We ought to be able to take them with anything.
I wasn't suggesting that the crown owns those corporations, but merely keeps them heavily regulated. For example, a single corporation (or guild) may control the entire agricultural sector, but they have a large amount of smaller companies underneath them that they manage in competition with one another. If they should move away from this, to the detriment of the people, the crown steps in and swaps out the people at the top. If they step off in the other direction in that productivity begins to fall, the crown also steps in. The best of the corporations are very wealthy individuals and constitute our middle class (roman middle class, not modern middle class), the workers at the bottom are obviously the lower class, and the noble families (effectively social guilds) are the upper class and have arbitrary power of regulation. The nobles themselves are kept in line by the power of competition. Fail to keep your corporations (guilds) in line and you piss off the people. This makes it hard to recruit out of the general populace for talent, and creates opportunity for rival families.
Essentially, while commoners don't vote, the extremely talented can influence the balance of power by choosing which family they join, which gives them influence over the corporations. If you refuse to recruit plebs who want to help thier people and regulate, you fall behind in terms of talent and support, and someone else will exploit that opportunity.
In the end though, it's all just fluff, and probably won't affect the game at all. Personally, I feel like the victorian esq steampunk setting calls for a bit of brutality and imperfection in our society.