If you think about it, Talabecland ought to be a rich and prosperous province. The Talabec, a major trade route passes through the province, making it the gateway between the northern and southern Empire. The river must be useful for irrigation as well, and with its large land area Talabecland must contain a lot of arable land. As Talabecland suffers no major military threats, like Chaos in Ostland, beastmen in Middenland, or orcs in Wissenland, you would think they would have the peace needed to become a major power.
So, I would think that it is an economically powerful province. Due to all that land area, I imagine agriculture would be particularly important, and that Talabecland might well be the breadbasket of the Empire. This would make the province particularly wealthy, or at least its nobility wealthy, but also account for a reputation as a bunch of backwards farmers. Other than Talabheim, which is not technically part of Talabecland, the province looks to have a mostly rural population, which would explain much.
Regarding the rulership, I was under the impression that the Krieglitzes still rule in Talabheim, though not in Talabecland. I should think that there are many Krieglitzes throughout the province, as a successful noble family would surely intermarry with as many other nobles as possible. As such, Gustav von Krieglitz could still rule some settlements without necessarily being the Elector Count. Perhaps Helmut Feuerbach married his daughter, thus becoming the Elector Count legally and without breaking the chain of succession? Sadly I have unable to obtain Sigmar's Heirs and cannot check what's in there to speculate, but the problem doesn't look unsolvable.
