[Tuor in Gondolin]

Sam as not very bright seems to be inaccurate. After all,
Mr. Bilbo taught him his letters, he had a good memory
for tales and songs, and an inquisitive mind.

A problem (and interesting variant) with Sam as ringbearer
is an inversion of the (at least initially) class structure of
Sam as Mr. Frodo's servant (and in Tolkien's mind Frodo's
batman).

But as to Samwise as ringbearer, a good case can be made that he
was more suitable, especially in his common sense and realization of
his limits (Samwise the greatest gardener in the world--- no way!).
He would of course have eventually failed to destroy the ring
(see Letters). But here Frodo might have been more perceptive
and helped dispose of it. I don't think Sam would have killed
Gollum, partially due to Frodo's intervention.