He made no reference to thousands of years of domestication in the posts I read; he referred to an individual mountain lion that been trained / domesticated. If he had been making the point you are making, I might have responded slightly differently, but it wouldn't have made his point more valid.
It depends on how domesticated they are. For instance, it is widely debated exactly 
how domesticated cats are - and certainly everyone agrees that cats, which are thought to be essentially self-domesticated animals at most, are far less domesticated than are dogs. I think we've all heard jokes about how we're lucky that cats aren't as big as wild ones, right? 
So, if you managed to domesticate a population of a large species of wild cat so that it was as domesticated as a dog is, then yes. I would feel comfortable with that. If you managed to domesticate it only to the point that our house cats are domesticated, well... no. I don't have a death wish.
And pibbles aren't "massive:. They're comparable to Australian Shepherds or Boxers or Collies or a GSP; all breeds typically in the 50 - 70 pound range