You’re assuming everything scales linearly, which is not necessarily accurate. The square-cube law rains on many people’s parades.
I can see how you’d think that, but I’m really just asserting that these specific things scale well enough to still work at post-Panamax size.
A bigger challenge would be sourcing enough shantymen to be feasible. I’m not sure that the world has sufficient production capacity to provide the necessary rum for more than a handful of ships.
I have it on good authority that the Wellerman will handle this issue, along with any concerns with tea and sugar supply