On that count, I completely agree. In the classic series, they never appeared every season except during The First and Second Doctor eras. After that, there were nice breaks here and there, although both had one huge gap.
The Daleks: The Second Doctor's season 5 entry The Evil of the Daleks in 1967 to The Third Doctor's season 9 entry Day of the Daleks in 1972.
The Cybermen: The Second Doctor's season 6 entry The Invasion in 1968 to The Fourth Doctor's season 12 entry Revenge of the Cybermen in 1975.
That being said, they were briefly glimpsed in The War Games (both), The Mind of Evil (Cybermen), and Carnival of Monsters (Cybermen), to name a few, during those gaps.