In Skirmish mode a stalemate seems to exist if no one has attacked or capture a building in quite a while. You get a 1 minute warning to quit stalling or else a stalemate will occur.
Taking enemy bases is certainly quite difficult, but there are options. The Shaman has skills that can lower damage you take and remove enemy units from the equation, the Warlock has skills that can remove single enemy units and bomb static defenses, there are Kamikaze troopers, and of course there are Devastators with siege mode.
Well I do indeed appreciate that all this stuff exists, but the defender has access to all these tools also. Defence is always a stronger position to be in, in all RTS games. However generally you have to defend multiple locations at once, which requires you to spread resources. Currently this important point becomes moot as soon as the Population Pool is depleted, you only need to defend 1 location and defence becomes very strong.
I feel like the balance between defence and offence is fine for the main part of the game, it is only after the population depletes where defenders become too strong.
I'm still curious what exactly this stalemate does, I personally haven't seen it. How does it determine who wins if it occurs? It would make sense for the defender to win in a campaign game, but in a skirmish game how does it determine the victor?