I don't think we can tell exactly how many people worked on some of these projects, it could have been far more than 1-2 (which is the implication given for some of the games), not to mention a few of these were being worked on for a year or more, and some even for 6 years on and off.
In any case, it certainly doesn't sound like a very efficient system or work flow, and also might go to explain how something like Sea of Thieves could come about.
In the thread over on the other forum, I believe it was stated that there were a total of 20 cancelled projects around that time, some that had a fair amount of time and money invested in to them, but which were ultimately rejected in favour of more child friendly or Kinect orientated projects.
And I'm telling you this is pretty normal at most devs. Valve, for one, has dozens of projects that went nowhere. The thing is that a lot of devs and publishers are incredibly secretive, and the cancelled games are often related to existing IPs (from games or otherwise) which makes talking about them or publishing material from them a lot more complicated. Rare has always been a very open and honest company, hence we know about their struggles, their ideas and stuff far more. For example, you had to hear from anonymous sources that a giant Star Wars project they worked on for years (one that has never been officially announced) has been cancelled - without Schreier's incredible work we would have known fuck-all about it, and that's a game that costed EA tens of millions of dollars possibly.
And, for the record, those child friendly Kinect orientated projects sold a lot, far more than a Banjo 3 or Kameo 2 would have generated in terms of income. Not to mention it's easy to put the blame on the publisher for cancelling games, like the early gut reactions that we had at that Star Wars game, where it ultimately turned out that the development was a fucking mess and was not going to be completed for many years, if at all. Given Sea Of Thieves' lenghty development cycle and the fact they launched with a limited amount of content despite everything, I wouldn't bet large sums of money on the fact they had 20 projects going awesomely and then evil Microsoft execs came in and cancelled them all. Usually the truth is somewhere between the extremes.