You can watch Bungies GDC talk about designing Destiny and how the game started out full high fantasy. I am not saying you are wrong and im sure some of the lore ideas came from unused Halo or work in progess halo stuff but I don't think it was ever a "Halo" game they reskinned.
funny thing is if it was titled Halo:Guardians it would be getting 9's and 10's
Oh yeah I know I'm probably wrong but in my mind it all fits.
Oh there would be far higher scores for sure if it was Halo.
I would give it at least an 8.5 as is. There are a ton of problems but when it comes down to it I haven't had this much fun playing a game in a long time. (playing with 3/4 friends of similar levels)