I have been testing out the Montana and its AA and honestly its not that great, I was in a fight vs Lexington and in 3 strikes he did on me I shot down 6 planes. Did 25K dmg I had the AA skills...
I had "most" of my AA intact in the first strike 85% next two it was down to <45% because each game has 3 Thunderers shooting HE all day long at you.
And in my opinion that is a fair representation of a ships AA ability, you can't only test it with 100% AA and the plains flying straight at you through flack.
But a bigger problem for me is that I don't really like the skills I can take for my Montana, they are all so... crap. And If you look at the Montana skill guide. https://wiki.wargaming.net/en/Ship:Montana
None of the skills are Key: ★★★ - Extremely Useful.
I feel like they don't add much for the Montana especially 5 points in AA is not worth it at all. And I hate the DeadEye skill and all BBs are fleeing to the top of the map.
I chased have 3 BB's to A1 and they sit desperate to get that sweet sweet DeadEye boost.