Wasn't the kingdom carving aspect from Brandenburg, rather than within Prussia?
More to the point, how are they going to survive the rise of the Ottomans (or something similarly threatening)?
Well, let's say Brandenburg-Prussia ... as for the Ottomans, the Teutons would need to survive the Mongols first, so let's not go so far ahead.
Well, Wallachia became Ottoman vassal only in 1415, and Teutonic State would likely fare better. Perhaps situation would be similar to OTL in Prussia - TO being slowly defeated by Ottomans, resulting decline leads to revolts of cities (like with Prussian Confederation), which finally turns remnants of Teutonic state into secularized (maybe even protestant) vassal of Ottoman Empire.
Why would it fare better?
I mean, what does it have that would stand up to an Ottoman army more successfully than OTL Wallachia?
I think the difference so far as the Ottomans or a similar power is concerned is more in the details than the balance of power.
Well, for starters, Wallachia was a young state when it met the Ottomans. The Wallachian Teutons, on the other hand, will have 200 years in their back when the Ottomans come knocking on their doors.
Romanian will resemble french more in that scenario.
Or more Germanic, actually...
I like a Catholic Romania actually.
Hold on guys, Romania as we know it might not exist in such a timeline. Take a look on the old Prussians for an example.
I mean, I feel sorry for the poor Orthodox Vlachs living under the Teutons. There are some rough times ahead of them.