Counter-point.
IG can bring 8 plasma guns to the table in matches. Should Astartes get access to 8 specials? Should Necrons get access to a plasma gun or two?
Hopefully, the rules are balanced between the factions using their available equipment. Changing that, especially in MATCHED play, would be a bad idea.
That said, you’re describing a PERFECT example of narrative play. There, the only limitation is your opponent’s permission. That would be perfect for a suicide mission scenario where the Last Chancers are put up against incredible odds to achieve a mission. Go nuts with the
ML there.