I think that the decoy could do without the stat buff, with a result of 2|1 at the very most.
Note that the card Firefly Queen and Pharaoh have no changes upon upgrading, the fact that the spawn is balanced (Firefly to Elite Firefly, Scarab to Elite Scarab) is enough to balance the card.
And wouldn't it be cooler if the decoys were 1|0 and 2|0? If you did, then you could probably lower the initial and ability cost of Stealth Flier - so it would be easier to fit into a deck - and it would synergize with boneyard/bonewall/catcher/virus. Not to mention the thematic reason (who puts a working engine and a capable pilot in all 22 decoys that you produce from one plane?)