Ulfric can't be held responsible for the Thalmor being [censored].
Not saying he is. You could also say he can't be held responsible for the people that fight against the Stormcloaks. That doesn't mean he's innocent. The Thalmor very clearly want Civil War or something like it in Skyrim as the game makes clear. Ulfrics actions play right into their hand, which isn't something one can dismiss. It doesn't help poor Ulfric's case that he didn't even try to do things peacefully (of course, doing that wouldn't make him High King if it worked). I can't really call a guy who instigates a civil war that may well have been unnecessary a "realist" or even someone respectable, not if he didn't even try to avoid it. The man has some major faults, and a lot of people died because of it.
Take the Skyrim situation, if things really were bad enough to leave the Empire and the Empire was stretched then, then we have the makings of a really popular rebellion. Maybe that would have taken 10 more years to happen, but it certainly would have been worth it if it didn't result in a civil war. Given how Hammerfell was handled, if all of Skyrim was united the Emperor probabably would have just let them go. I know some people hate comparisons with the real world, but I think valid ones can be made. Popular rebellions and movements needing a decade or more to gain widespread report are common enough. I'm not saying Ulfric could know all this by any means, but the man could have at least TRIED not to split Skyrim in two; he didn't.
Of course, judging the Jarls is difficult and I think it is perhaps easy to take the Lore too seriously. There seems to be quite a bit of it that is based on a sort of twisted/macabre humor by the devs. The Jarls are pretty much a list of bad/weird leader tropes (and not in any complicated or interesting way, generally). The TES universe tends to skew this way in general -- note the work put into all the evil questlines, whereas despite the fact you are a hero, there's not a lot of involved heroic work (nothing like the Daedric quests, Dark Brotherhood, or Thieves Guild).
I think there's also a potential problem with holes in the lore and worse, sort of rushed programming that can lead to judging things too readily. To me it is sometimes hard to tell what they intended verses what they didn't want to/think about fleshing out verses what is poorly fleshed out or looks bad due to "good enough" scripting. Ulfric's apparent apathy regarding the Dunmer and Argonians, for instance. Is that because he doesn't care? Did they decide they didn't want to go into his racism? Did they just run out of resources and didn't have time to put in him talking about it? I don't know, and it could certainly be that they intended him to be troubled by it and unaware of abuse by Nords (though that seems unlikely to me). Perhaps similarly he isn't as power-hungry as he appears (and unlike what most everyone says about him). There's enough stuff that's done in a rather shallow manner in the game that I can't be sure.