I've seen huge AI SoDs on Prince level as well, though in Epic speed. But it could've been because I invaded Zara's (who was my equal in power but he was lacking techwise). I had planned my attack wisely or so I thought, surprise attack on one of his bigger coastal cities. A cakewalk to defeat the 2 or so rifles and a few more obsoletes he had defending the city, getting my troops into the city, my defense in that city was ~10 infs, 4 machinegunners, some tanks, plently of cannons and cavalry. The next turn he hit me with troops that took my computer 10 minutes to resolve all the battleanimations. Everything from Pikemen up to curiassers and rifles. He finished my attackforce and retook his city, when I studied what troops he had left, it was still a quite impressive stack in that city and outside it. Ofc I reloaded, delayed the war a few turn to improve my own SoD, now with focus on more of my newly aquired unit, tanks. I beefed up on defensive forces as well. Declared war again, took another city which was easier to defend (alas, he couldn't reach it with his SoD in one go, so my tanks/cannons would have a first go on his stack.) Well, even with alot more defense and a good chunk of his SoD dead from my strike, he did beat me anyway. Third time though, I divided the forces, hit him from two direction, while I lost in one end due to his SoD I got a good foothold on the other end of his continent and could start the invasion.
Ah, maybe a bit off topic but anyway, SoDs can be huge in BtS, good or bad but atleast it gives some interesting battles...