I actually think Red Card is a good idea on Forretress, but only in certain situations. For example, like you said, saving your team from a sweep, or if a pokemon deals 60% damage, then gets shuffled to something that can't touch Forretress.
Sure Lefties gives you 6.5% per turn, and is pretty much Forre's only form of recovery, but the red card can surprise enemies and potentially save you from getting swept. In order to counteract Forre's lack of recovery, why don't you try running a wish passing set like Salamence or Jirachi?
Salamence (F) @ Leftovers
EVs: 252 HP / 192 Def / 64 Spd
Bold Nature (+Def, -Atk)
- Dragon Tail
The first set I recommend is Salamence. It's synergy is perfect with Forretress, allowing you to send him in, wish as they send in an Ice, Rock, or Dragon attack, then switch to Forretress and get healed.
The move set is simple. Wish to get recovery across the team, and protect if you need the recovery your self. Dragon Tail is for Phazing, things like Conkeldurr and Scrafty. Flamethrower can deal with all the steel type walls like Ferrothorn or Forretress. The EVs are to out-speed max speed Scizor just in case, you also out-speed Adamant Breloom and Tyranitar.
If you want more instant recovery, you can do Roost over Protect, which would take advantage of out-speeding Ttar to remove your Rock weakness.
Jirachi @ Leftovers
Trait: Serene Grace
EVs: 252 HP / 192 SDef / 64 Spd
Careful Nature (+SDef, -SAtk)
- Iron Head
- Body Slam
- Fire Punch
Jirachi is arguable a better wishpasser than Salamence, but I think Salamence is better because of how his synergy is good with your team. On top of that, Fire Punch doesn't pack as much power as Flamethrower, and the Phazing with Dragon Tail is nice.
The EVs are straight from smogon, with 64 Spd to outrun Max Speed Scizor. This set provides heavy utility to your team, being able to spread Paralysis, and ParaFlinch allowing you to heal yourself with wish, also.
I personally recommend you replace Metagross with these, but that's up to you, you can test whatever you want.