What silly arguments against more than 2 Crew on a Sloop.
You know even on the Sloop, you carry a limited amount of Planks ... those aren't "Infinitely Deep" Barrels. With the limitations being 3:1 (Cannon Ball : Planks)., this is assuming no Ramming or Beaching occurs... you should always have more shot than repair capabilities.
Because the Galleon doubles these limits, honestly that makes them more "Invincible" against Sloops... which they can't out-manoeuver but they can out-run due to them being substantially faster.
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Now personally what I'd prefer to see would be for the Tavern to be used for recruitment. So when you first log-in you enter the Tavern (which could be a "Safe Zone" inside) where you have no equipment but a pocket full of Gold...
There should be 4 Classes of Ship. Rowboat (1 + 1 / Loot Barrel), Sloop (1-2 man), Frigate (2-4 man), Galleon (3-6 man)... they could down the line introduce different variants of these; say like a War or Merchant variation as part of the Ship Upgrade / Customisation to better suit what you (and your crew) prefer to engage in.
(For the Larger Ships, 1-2 Rowboats could be added for traveling to and from islands)
How they can balance the Crews is simple... Loot Shares.
Where Gold per Crewmen is merely divided by the Number of Crew, on top of this though the Unlock Costs could also be increased respectively. Plus the Unique Treasures (such-as the Voodoo Skulls) could only benefit a single crewmen, thus add a little tension to who gets to hand it in for the reward / unlock.