The Tom Baker era was hardly the B&W era, but the Hartnell seasons did run longer, but then most series back in the early '60s did.
Brendan acknowledged that; he said "playing the Doctor now is far more intense and time-consuming than at any point
since the black-and-white era." And one should note that in the demanding B&W era of the show, the typical time in the role of the Doctor was... three years. Only the less intense production schedule of the 1970s deviate from the pattern of three years per Doctor.