Clash of the Titans.
I don't know about you, but the Bastion hardly did anything in that mission. It was bombers all the way. If it had been nothing but the destroyers (no bombers, no fighters), the only way for the Demon to stop the Orion would have been to literally get in the way.
I can't think of any missions in FS1 where the real threat to a destroyer was another destroyer's guns. (Heck, even a cruiser was pretty safe from a destroyer's guns). It was always bombers eating destroyers, and assault fighters eating cruisers.
The only display of 'real' firepower by an Orion is in the FS2 opening cinematic, and it's impossible to judge just how effective it was being.
---
I figure that a FS1 'destroyer' acted much like a fleet carrier (with a very distant secondary role of a gunship.) Stay hidden somewhere and feed strike craft to areas of engagement. In this case, a significant portion of its aero-group would be bombers.
The FS2 destroyer has a much more balanced role as a battleship-carrier (thanks to those beams). It is able to directly support its aero-group in battle, providing the heavy striking power needed to hit high-value targets. Since the ship itself can be the 'big gun', it can get away with a reduced bomber complement.