They could also sacrifice Mothra to KG early on to show the bad guy's power AND throw off audiences. Of course we know that an egg would come into play and hatchlings would emerge, or perhaps they could go with two larvae and have one remain in worm state while the other pupates into adult form for the final battle... or one Mothra (female) and Battra (male) could emerge, which I think could be pretty cool. This isn't Toho's universe, so anything's up for grabs here.
I do agree that they need to include other monsters from Toho's stable. Heck, Legendary could've licensed Angilas, Gorosaurus, Varan & Titanosaurus for what they paid for for Mothra alone, probably.
I long for a team-up with Godzi & Angilas again. And for pete's sake, honor Banno-san and give us a new & improved gorgeous CGI Kaiser-Hedorah!