1) Broly kills him. Paikuhan's performance against Cell, considering he couldn't one-shot SS Goku, seems to be a case of sucker punching.
2) This is a blind spot in DB. We don't know how Gero compares to 19 or how Piccolo compares to Freeza.
If the androids are even, Gero, as 19 was, would be outclassed by a sick SS, who could be at Namek SS level. In that case, Gero vs Namek 100% Freeza would result in Freeza having the edge until his power starts to drop. Mecha Freeza, at full power, should defeat Gero.
But let's pretend sick SS > Namek SS. Here, Gero might beat Namek Freeza just like Goku did, and against Mecha Freeza we would have a pretty even fight.
I guess it depends on how much weaker Goku was due to the heart virus... considering Vegeta beat 19 who had absorbed Goku's power and his own power, and Vegeta should not be that much stronger than Goku, I'm inclined to believe the heart virus weakened Goku a great deal.
That, in terms of power, in practice, Gero would easily absorb Freeza's attacks and get the edge.