No, it was changed 1-3 weeks(can't remember how much time) after this patch so that
"in-game credits" "Plane & Anti-Air attack" also counts as attack and will receive 100%
But overall, if you don't get attack(with guns or planes or AA) you will receive 30% exp.
for all sailors.
PS. If you get below 15K in-game credits per game, yes you level slow. If you get 30K
in-game credits per game, you level equivalent to a 100K damage in a BB per game(so
pretty good).(this without counting normal attack)
The method you use to get that high in-game credits is up to you.