Yea, tight's all right. A time cap might be a good idea, I'm not yet familiar enough with the map to make much of an opinion on that. The Sevastopol thing really is the only thing that bothers me, design-wise, it's certainly not typical of any variant I can think of that a player can have any given SC without anyone being able to take it from him without crippling himself. Building any fleet at all on that map is very taxing, but building two, on the same sea? Better have *really* trustworthy allies covering your ass! And given the map, you'd have to be pretty foolish, imo, to trust your ally and do this.
Can't really think of any specific fix for this, though. Removing it completely, I guess?