Also, from further out in footsies, f12~overhead bop is gapless. You have to do it max range though so f1 would whiff first. Only problem with 22 and f12 is that they both start with highs.
I don't think Butcher needs to worry about gaps anymore though. Interrupting gaps with armor doesn't take 30% like it used to. You might say that was an indirect buff to butcher but it's really not. Losing armor on the ex overhead sucks hard but his other armor is useable now. ex db1 having 2 hits of armor is really nice because the move is so damn slow that it will beat other 2 hit armor attacks because their armor times out before the chainsaw hits! ex db3 does 21% and has 1 hit of armor while his command grab does 20% and has 1 hit of armor. The command grab is so fast that it rarely loses to armor breaking strings, but it can happen.
So, going back to gaps and being +2 and armor... I think Butcher has a mixup game with his armor, (oh, low, grab) but it's all unsafe. It's probably better to stick with command grabs and his safe strings for mixups. Save armor for getting in (ex bf3) or wakeup/reverse pressure.
I'm not sure what the safe low you are referring to is... probably b12. b1~oh bop is probably a decent safe mixup now, even with the gap. Also, f3~oh bop is a low, oh that is +2 with a gap while f21d22 is a safe overhead string. You can cancel f21d2 into the +2 df2 as well.