oh, i get beat now and again haha.
although it looks like you misinterpreted my info.
For the reference of other players who pay attention to forums, let me simplify it for you. If you have a defense crew, with all pirates having 10 or more cost, you don't have to worry about your base defense until it gets to the same cost as your "highest cost" pirate.
So if I had a crew with costs 15, 25, 41, 22, and 16, and a max DEF stat of 200, I won't have to worry about my defense weakening until 41 DEF.
your def will never weaken until it is below 10 def.
The only time it will weaken before 10 def is if the max def required for your team is less than your current max def.
For example, if you have max 200 def, and run a team that costs 150 def, that team won't weaken until you hit 9/200 or lower.
But, if you have a max def of 100, and run a team that costs 150 def, that team will be weak as only 100 def worth of pirates on that team will actually defend, and the other pirate's stats will be 0.