"Had the G55 been adopted its very very possible the US would have had to abandon daylight bombing in 1943....."
I think your mistaking something for an Me 262, which is the only a/c that could have had the effect you are implying.
The G55 was a fine fighter, 1st class, one of many that both sides flew, lets not get carried away into fanboi-fantasy-camp over it.
...and the Fw190 was the premier bomber killer for the LW in 1943/44, and was even more heavily armed than a G55 was. Calling it a "pre war design" is beyond cherry picking your data. You can hardly compare the Fw190 prototype to what was flying in 1943.
I will leave it at that, since this isnt the thread for it.