No. The old behavior was that carriers under direct attack had the 50% penalty. But with that the carriers were able to keep spamming strike craft and it was pointless to try and kill the fighters/bombers because the carriers just kept spitting them out.

So IC introduced an "in combat" penalty of 25% (dropping to 15% in the upcoming patch) that all carriers suffer when there are hostile ships in the current grav well. The 50% under direct attack then applies on top of that as a multiplier, rather than a linear (which would've brought it to 25% total rather than the 37.5%)

So I take it this applies to all sc capable ships including sbs.

Not sure about starbases but the 25% reduction with enemies in gravity well does not apply to capital ships from what I've seen. They only get the 50% from being under direct attack. Only light carriers seem to get the stacked 38% reduction. Thanks for explaining where the 38% comes from Annatar.