No, not overrated. Rather, his successors are underrated in comparison. Wrongly, and no fault of theirs or Sean Connery's. One reason, I think, is a consensus amongst some film critics - those who can be bothered to "slum it" by actually missing a night in the art-house for a trip to the multi-plex - that Bond stopped being something worth watching when Connery quit the role, and that all else after is just the "same old same old" with someone else going around calling himself James Bond.
Admittedly, Daniel Craig has impressed some of the self same critics enough to warrant the title "The Best Bond Since Connery", but note, not "The Best Bond".
It is a pity this view still persists forty years on, because all the Bond actors brought something to the role and deserve better than tiresome comparison with the first, a comparison I would imagine Mr. Connery would also find tiresome and pointless.
All of us have our favourite Bond actors and Bond films - and some favourite films might not necessarily feature the favoured actor as 007 (OHMSS a case in point with me.)
Besides, unusually in the world of cinema and celebrity where many fans flock to see their idols on screen, the star of the Bond films has never really been the actor in the role but always "Bond, James Bond".
^^^ this.
Unless the current Bond is proclaimed to be "The Best Bond since Connery", the franchise has failed. Craig and Brosnan (and if the books I've read are true) Dalton were all called this by different people during the initial height of their respective eras.
For me Craig eclipses Connery, but Connery's significance to the birth of the franchise and the zeitgeist of the 1960s could absolutely ONLY come from him. In that sense, he is the one-and-only.