Some ideas that will probably get down voted because they are far fetched:

Fleet warp changes for kitchen sinks. SciFi explanation; all ships make a similar sized warp tunnel. Frigates move through their warp tunnel quickly because of low friction inside of said tunnel and battleship's and capitals warp slowly because of large resistance to the sides of the warp hole. Flying frigate's with larger sized ships allows them to share warp tunnel space, slowing the frigates down but greatly increasing the warp speed of larger ships. The more frigates you have the faster you warp.

Reasoning: this will let small fleets field battleships and battlecruisers with wolf pack type fleets. Ships like dictors interceptors or tackle ships can either opt out or be immune to slowing affects.

Change bombers so battle ships are useful again. (Super known I know) I don't fly big blobs but how viable would it be to drop mobile refit stations all around so that if a bomber wing shows up everyone fits specific resists? You can't take off hardeners but you could take off heat syncs and passive damage modules. Or a command ship link that would give insane resists to one type for a short time. Consuming huge amounts of cap and making them immune to cap transfers while active and for x seconds after deactivating

Finally the question should be asked "what do frigate's bring to a fleet" there are interceptors which are brought to big fleets. Then the are logi, inherently used only in frigate fleets though an interceptor speed logi for inty repairs would be cool but hilariously broken. There are ewar ships that are only good in small gang. And there are dps frigate, and if you want to go dps you should stick with the doctrine. Finally you have bombers, who are brought to big fleets. So 2/4 of the major types of frigate's are brought to big fleets.

Now cruises. HACs and t3 are largely represented and logi are always there. The only thing not taken are recon ships who are inherently small gang.

And battleship's, these guys are killed so easily by bombs it's sad. So you can't bring them often.

Two really radical changes that may help but probably hurt: One cynosaural beacons must be up for one (or more) minute before you can jump to them, allowing for sub cap counter play to stop a drop or reinforcements before they happen and requiring a force already in system to hot drop. I am imaging a situation where blops have to be snuck in first caring a normal cyno then the stealth ship fleets have to defend for one minute to start an offensive. Though this give defenders a big advantage.

What If cyno bridges and portals worked like wormholes but were system wide. Only xxxxx mass can exit a solar system per hour. Forcing capitals to be decentralized. Though this also gives a huge defenders advantage and make retreat not an option