I never get the problem people would have with a true historical that didn't feature a monster? It is a bit silly to suggest that every era of human hisotry was filled with aliens, and I don't see why a pirate, or a king, or an Aztec priest or a 20's mobster couldn't be just as good a villain if he didn't have a Dalek hidden away directing his every move!
I'm a huge, very long-term Doctor Who fan. However, I have to say that I'm just fine with the lack of pure historicals. One of the reasons I love Doctor Who is because I enjoy SF. And, yeah, I know DW isn't pure or hard SF, but I do enjoy those elements.
Also, the pure historicals tend to be about simply getting away from a tough situation. I saw Reign of Terror and it was mostly about getting themselves free, reunited, and back to the TARDIS. They can't really change and fix things. They're also less rationale. If history is unfolding naturally, why would
the Doctor interfere? He pretty much lets history unfold naturally unless there is outside interference.
So, they tend to have their hands tied storywise and they lack the SF elements that I personally enjoy.
That's my take in a nutshell!