I think the assumption is ships are nominally close to their DP value in terms of effectiveness added to a fleet. In an ideal world, frigates are worth their DP, or if they're not, you buff or nerf them until they fall into the right benefit to the fleet. So a skill specifically just buffing frigates in general is possibly not so interesting under that assumption. Why frigates in that case and not cruisers? If they are in fact worth their value, you should already see them included in fleets.
Given the AI's has more difficulty when outnumbered or flanked, coupled with advantages in late game gained from capturing points early in a fight, many frigates are likely worth their DP, in a matchup that ignores skills.
However, if ships are all worth their DP and officers are percentage based buffs on top of a ship's value, that means you'll always want to put your officers into your most expensive ships first. Which generally is capitals, followed by cruisers. A 30% increase on 20 DP is a much better investment than a 30% increase on a 4 DP investment.
Wolfpack tactics is intended to help compensate this a bit and create more varied fleets. Ones where you might actually choose to put officers in lower DP ships, since you're getting closer to the same benefit. So now you've got like a 50% increase on a 8 DP investment instead of a 30% increase on a 20 DP investment. So making Wolfpack tactics also apply to unofficered frigates is somewhat missing the initial objective, namely spreading officers around, as opposed to generally improving all frigates. If frigates need improvements to compete, they should be buffed in their raw capability, not have a skill patching it up.
Carriers are in a different boat because they scale faster with numbers than frigates or most ships in general. Fighters (and missiles) can't collide, and can shoot through each other, and thus nothing is preventing a critical density of them coming together and just overwhelming one ship at a time. Frigates still bump into each other, can't shoot through each other, and have short range, resulting in a smaller enveloping circle. Thus the carrier bonus scales to give a fixed benefit that doesn't grow with fleet size, so it doesn't help that non-linear growth as much.
The issue Thaago and Alex are trying to address is Hyperions are nominally worth 15 DP, which is more than some Cruisers. They already have a high DP value, and assuming it is accurate, that is a fairly good reason to stick officers in them by itself, without much extra push from Wolfpack tactics. It's quite reasonable to imagine officers being placed in Hyperions even if Wolfpack tactics didn't exist, which means a flat application to all frigates is going to make Hyperions much better officer value than nearly any other ship in it's DP range. More so than Furies or Eagles, for example.
I guess one general question to ask is, are Hyperions actually worth 15 DP by themselves, in a comparison that doesn't include Wolfpack tactics. This is definitely a nerf to Hyperions, but the question one needs to ask then, are Hyperions with Wolfpack tactics too good and need said nerf? Or do they need to be buffed to be actually worth 15 DP? Similar questions should be answered for the other frigates.