Scale beetwen Heroes/Gods/Champions etc and minions has always been off in almost all MOBA games I've played. So it isn't something I really take into account. The pathfinders (or at least human soldiers) in the trailer are way more closer to their in-game model than these alien-robots (still think they're not cyborgs) are close to the Drone model.
I agree to a certain extent that a cinematic trailer isn't here to depict with a perfect accuracy the in game units. But if you do something too far away from what they look in game, new players might be disappointed as the universe game isn't like what they saw from the trailer. It isn't necessarly that way but it's a possibility. Kind of a false advertising ? (I'm exagerating of course, but I hope you'll see what I mean).
As for why cyborgs would not be in the trailer then, there's a ton of possible answers but I'm not one of the dev so I can't provide anything accurate.
You're right, we don't have ebough informations to deny or confirm this point (WE NEED A DEV TO ANSWER NAOOOOW !).
But I'm not making a suggestion (there's already topics about it, I even answered), rather discussing and making theories about this trailer with you all guys, as well as appreciating the work made behind this amazing trailer (Did I mentionned that these aliens-robots look cool ?).
Drones are indeed melee units, yet they aren't using any blades. They possess a laser shotgun like cannon on their right arm.