The trouble with this story is that you are depending on your guides version of events. That his guy was there earlier. That the other guys showed up late and set up down the field. Unless you spoke to members of the other party and they admitted to slipping in last minute or you saw it happen, it's a he said/he said situation.
I'll say I've hunted with Grey Bruce, and had a great time. We were hunting turkeys and passed on the first spot they had in mind because there were trucks parked at the access. We headed elsewhere and both of us shot a bird that day. It was a great time.
I found a bit of drama about these competing outfits online before my hunt and asked the owner about it. He mentioned that your guide had worked for him in the past and had set up a competing business. He only said "sometimes partnerships don't work out". other than that, he didn't mention anything bad about the competing company.
I'm not saying it didn't happen the way it was explained to you, just that we don't know the entire situation.
Ultimately, it's a guides job to make sure that you have the best hunt possible. If I'd paid a guide to take me out and we ended up on a crowded field, I'd be a bit disappointed in the other group for crowding us out, and my own guide for keeping us there. Anyways, hopefully you get a field next fall that's empty of people and full of birds.