From personal experience, I highly advise not to do this. This has happened to me and my music, though without my consent first, and it did not yield well. Here are my points
1) Regardless of what the state of their channel is now, it could become something big, especially given that they just started. A Culling dedicated channel could bode well for them, and viewers are highly likely not to click on links that direct back to you. Viewers just watched your montage on someone else's channel, a video which has been essentially ripped from you for almost no gain at all; viewers don't need to put time into your channel. You underestimate the significance of people who take other peoples work and post it on their own sites. There are people who make livings this way, however, they usually don't ask first. You've been lucky enough to be given a warning.
2) This is YOUR work. Your video. Unless this other channel is a partner with you or is sponsoring you, the best case scenario is that you get a few extra views while the new poster takes all the credit and TAKES VIEWS AWAY FROM YOU. You worked 50 hours on this you say? Get the most out of it by keeping ownership in your work. I used to make music; hip hop beats like the ones you would hear in Samurai Champloo. On soundcloud, everyone, aka a few dozen followers, loved my stuff! Recently, I discovered that a few years ago, several youtube channels took my music without my permission and posted it there. They credited me poorly. Everyone thought that the channel owner was the one who made the work. They got hundreds of more views than I would have ever had. NONE of those views were directed back to me on soundcloud.
It's tempting to give your video to this person, I know. It's cool to have your stuff featured. But this is not free press or an advertisement for you. This is someone taking advantage of you. If you were to talk to a lawyer or any business owner, they would tell you the same thing.
My advice, if you still want to move forward, is to make a deal to be a featured Let's Player on their channel. That way there is more of a human personality component to it. Then, people who watch, might want more of YOU, not the montage you just gave up for free.