FF is weird to me because depending on primary, its too strong, or too weak.
Bot/FF is a classic and is waaaaaay over Def at max level with an expensive endgame build
But Merc/FF is only at or around the softcap with Mace Mastery's Power Boost and pet buff IOs
Sonic is another oddball that can synergize well depending on primary
Demon/Sonic was nice because of stacking +resist and -resist, with pet inherents and pet buff IOs I was easily capping s/l resist at 85% and whatever their quirk resists were
Merc/Sonic was a slight upgrade to Merc/FF, but still not much synergy
And my Beast/Cold only worked because I PLed it to 50 for the pet buff IOs and access to hamis to really frankenslot Fog and Pets to really maximize +def to get softcapped