So I thought to myself about a scenario of "How would an invasion of modern day Earth from the Cabal go down ?"
Be it a scouting legion or the Red Legion, what do your think their strat would be ?
"It'd be the seven hour war all over again, except this time, we wouldn't even last seven minutes."
Joking aside, we'd lose with little difficulty from the Cabal. Our best option would be nuclear weaponry, which, unsurprisingly, the Cabal also have and then some. Even in the best case scenario where we best a few of their legions, we'd have no hope against the Red Legion in their prime.
Heck, in-game, we'd still be fighting the Cabal for who knows how long if Savathun didn't pull a Resonance Cascade on Torobatl.