These two toy lines share an odd connection. Both toys were made by Mattel and on the back of the King Arthur packages the cross sell art shows Hordak's Slime Pit from Masters of the Universe was planned to be part of the King Arthur line. (No evidence can be found that it was produced.)
I don't know how closely Mattel worked with the creators of the cartoon, but it seems the cartoon came first and Mattel was hired to make the toys. The figures are all made in a similar style to the Master of the Universe figures and the Boulder Basher features a recycled play feature from a Masters Toy. In the cross sell art the Slime Pit toy still features Hordak's face. While watching some episodes of the cartoon I saw the Slime Pit in an episode called Darren's Key. In the show it looks pretty much like the Masters toy, but Hordak's face was changed.
The fact that this toy that Mattel planned to recycle was featured in the show makes me think there was a lot more involvement from Mattel during the pre-production of the show. Perhaps the show producers came to Mattel with the concept and then Mattel came back with some mock-ups for the toys line. Then as the toys and cartoon moved forward both sides could incorporate what the other was doing.
The cartoon lasted two seasons and the toy line only had one wave of figures. I enjoyed the cartoon in the early 90's and since I found out about the toys I have been having fun collecting them. I wish both had lasted a little longer. Warlord Blackwing could have been a cool toy. Stridor and Night Stalker, the robotic horses from Masters of the Universe might have been interesting recycled toys for the Warlords. For more posts on King Arthur and the Knights of Justice check out this post about Sir Darren and Valor and this post about some of the other figures..