Yeah; they just got drawn out so long, what with the gap years and (in Smith’s case) split seasons. They have basically the same number of episodes; Tennant just got three extra specials in his gap year.
Compared to Hartnell who had, like, 40-episode seasons, each episode recorded just a week before transmission. So, the show was in continual production and broadcast for over nine months of the year.
Which makes the recent trend of producing thirteen episodes and then wringing your hands about how, well, we can’t expect the actors to stick around forever seem very strange to me…