I think straight historicals are difficult to make exciting without extenuating circumstances and it also can get pretty grim to show accurate history without the sugar of alien interference to help that pill go down. A lot of historical heroes were clearly terrible people so then you have the factor of not offending the people who lionize them while also not offending the peoples who may have been their victims. And then there are religious interests that conflict with historical information. etc. etc.
I could go for a few historicals where the outside/alien/supernatural influence is more hands-off or subdued and grew into legends like The Fountain of Youth or Beowulf or Bigfoot or whatever.
I would much rather show humans being awesome at something than bringing aliens into it to help out or being the cause of it.
At least Robots of Sherwood is a comedy so I can ignore the 'robots' part. It's shaping up to be Gatiss' best script.