While a decent fighter I have always enjoyed, the Fiat G.55 has long been overshadowed by the planes of other nations and especially is now with new additions. Compared to planes from other nations it is not appropriate for BR4, and should be downtiered to BR3 (where other nations have planes that still outperform it), allowing for it to be used more and fit in with other Italian equipment which does not go beyond BR3, allowing for better lineups.
Stats of other BR3 planes as well as the new Ki-100 which vastly outperforms it at a br lower:
Fiat G.55 (BR IV):
2x100kg bombs
x1 20mm MG 151 Cannon
x4 12.7mm Breda-SAFAT Machine Gun
660.95 top speed / 21.32 climb rate / 15.59 turn time
Ki-100 (BR III):
2x250kg bombs
2x 20mm Ho-5 Cannon
2x 12.7mm Ho-103 Machine Gun
591.84 top speed / 21.78 climb rate / 14.92 turn time
P-51D-5 (BR III):
2x500lb (226kg) bombs
x6 12mm M2 Browning Machine Gun (Late)
712.07 top speed / 20.84 climb rate / 18.32 turn time