Yeah, I don't think you would need Tennant if you had a good combination of folks behind the scenes.
You would still need the right person to be the Doctor but it would not be as much of a mess if they were just ok.
The sad part is there are alot of actors out there that I think could play the Doctor well or at least fine. Some potentially great. I just do not see them doing it or being asked in the first place.
One good choice to me was the actor who played the Governor on Walking Dead, and was like a fake time Lord in the Dr!