I’m using Frigates in my campaign games.
As a fighter lure, where a frigate with 4 anti fighter rocket launchers and two escort squadrons sit well away from my fleet to distract fighters. It seems to work so far and I can/have won battles against the main fleet with no opposition from fighters. If the frigate dies, well it was cheaper than trhe captured fighters I gain. The speed of the Frigates death seems related directly to the number of fighters it faces. I intend to cut back on fighter defences on my cruisers next.
As a LR missile platform. In the early game Frigates are easier and cheaper to build. In support (behind) Cruisers, they perform fine and seem to survive most “balanced” combats. I can get 4 fast missile launchers, armour & sheilds on a frigate for under 1000Cr & 70 odd crew. They aren’t particularly potent, but they are cheap & easy to replace.
As an occupying force a single frigate is enough to get improvements in loyalty and two is better & cheap.
As a trip wire force, currently I’m experimenting with holding back the fleet and using it en-mass where needed. Frontier systems are instead held by spare Frigates which retreat on contact with an invasion fleet. Its early days, but this strategy should pay dividends.
I’ve shied away from sacrificial roles for frigates, IMHO the campaign game is as much about husbarding resources as it is about ship design & fleet tactics.
Hopefully food for thought?