So what does everyone else think? Remember, this is based only on solo play against the AI, not multiplayer.
That's the big problem though.
The current AI is so bad that you'll easily can win every game by just using capital ships.
This of course makes using frigates superfluous.
I would really like to see less ship classes/types and more combined rolls for many of them. I don't see why a Carrier wouldn't have gun batteries of it's own. I don't see why a Frigate would be produced that can only bomb a planet or only defeat fighters, etc.
Balance mostly. Also specialization is often better then jack-of-all-trades ships.
The thing is, different ships fulfill different roles for which they need to be different. Flak frigates for example, need to be fast and agile with a high firing rate to effectively combat bombers and fighters. An anti-ship frigate needs to be sturdy and powerful. Those roles exclude each other.
A planet bombardment frigate only needs to be sturdy to survive long enough to destroy the planet, it just doesn't need weapons against other ships since even if it had those weapons, it would first not be very effective at fighting other frigates and secondly it would conflict with it's primary role which is to bombard planets.
Or the carrier, it's primary role is to field a squadron of fighters/bombers and replace their losses. For this it doesn't need to be very fast or powerful. It has to stay out of harms way to do it's role effectively, which is to carry fighters/bombers.
But all in all, most frigates get useful when playing against a competent enemy. Sadly, the AI is not a competent enemy, so the frigates aren't that useful against them compared to capital ships or even needed against them.