Marathon is great for what it is.
It is amazingly deep for how simple it appears.
And I am pretty sure everybody was aware of how sensitive the destiny pve community is and that they would not be attracted to an extraction game.
So I am pretty sure, after 12 years of the pve community crying about having to play PvP in some form or fashion, that bungie was not depending on said destiny pve community to play a pvp extraction shooter.