... How smart is the MC depends on the author.
How entertaining a dumb but OP MC also depends on the author.
Personally, I would pick the latter for a few reasons.
1. I Monke.
2. Easier to read, especially when played for comedy. For serious, it is probably other characters are just as dumb as MC or most likely even dumber.
That being said, writing a weak but smart MC does force the author to use his noggin more, like making a smart and possible solution, followed by the problem and covering possible plotholes. Sadly, most of the smart characters I come across came as braindead like the rest, including the author or worse, cringe. There is also the issue of faceslapping... why?