Actually the solution is both the answers provided by Urquhart1244 and vazandrew combined.
Thank you both for your insights, gentlemen.
Some comments on the topic:
Theatre is a dodo. As dead as.
Theatre itself is a package containing actual vids in various sizes, be careful not to throw it away but right-click Theatre, view content of the package and move the video's you want to keep to somewhere else on your disk or cloud storage.
Be sure to take the highest resolution version file out of the package.
You can import them into TV app, so you have a workable interface to display them on your mac. But that's as far as TV's usability goes.
iMovie doesn't have an export into Photos.
iMovie complicates the matter by offering ProRes, which outputs a MOV file. photos is not Better is to use HIGH quality, that outputs to MP4.
Homesharing is the best way of getting your vids to play on your appleTV box. It works with older versions of the appletv (I have a generation 2 box)
TV is the logical replacement for Theatre. I agree that Photos already has the bindings into iCloud which gives access to the video's from your devices. But using photos is too much overhead.
On top of that, photos trims video's that happen to be longer than 15 minutes!!
TV however is a very badly executed application. It stores its media in the iTunes ecosystem, You can't select thumbnails, and lacks a host of tools and features that enable the user to manage his content proper.
With all its millions Apple doesn't seem to be able to define a vision regarding a market leading set of tools on management of media. That's a let-down.
