To know that would require you to know how tits were percieved at the time of Renaissance, but I would never doubt your omniscience.
Desmond Morris had an entirely different theory about tits, as he opined in his book The Naked Ape.
He conjectured that tits were an evolutionary step to encourage pair-bonding, in that it encouraged face to face mating; an advantage to any species where there is a long period of dependency of the off-spring.
It seems that the twin globes of both arses and a goodly pair of norks, trigger strong mating signals in the male of the species, which may induce eyes to go out on stalks and trigger salivation.
He claimed that humans were the only species in which tits kept their protuberant shape once the period of lactation was over.
This might explain why arses seem to alternatively compete with tits, as erotic obsessions - the bustle didn't go out of fashion until WW1.
Vince Packard might be forgiven for his error, as he wrote his book in 1957, a period when Hollywood seemed to have made a fetish of big tits, and Jane Russell comes to mind in The Outlaw 1943.
Looking at Rubens' Venus In The Mirror (1613-14), can we conclude that he loved big female arses?