The first time I beat the boss battle, over a year ago, was with myself and 1 other pirate.
Weve even had pirates solo it back then as well.
Just noone talking about soloing it now I do not think.
I dont think they have changed it at all actually, I think pirates are just getting better at it.
Sure you may have had a few inexperienced, but it doesnt take a but a couple high level cannons to do the trick with a decent BB savvy sailor at the helm.
Luck is also a factor
One thing that I do also know for a fact, the BB does modify its level of difficulty when it launchs (always has), based on the number of crew, and thier notoriety levels.
If you have low level pirates, and fewer pirates it is easier, the ship does not take damage as quickly as with large high level crews (in theory it is just as hard though due to having fewer, or lower leveled pirates).