But presumably a track offset would be no more 'deemed separated' than a normal own navigation track..
But is this about deemed separations? I'm an approach/terminal controller so maybe there are some differences in the en-route environment and the related procedures but....
The only separation that matters is the appropriate radar separation (in my world, that's usually 3NM) and my job is to make sure the aeroplanes don't get any closer than that. As long as I do that the bosses don't bother me - and, broadly speaking, the bosses don't care how I do it. Getting my controller licence and certificate of competence, hopefully, has equipped me with a wide repertoire of control techniques to do the job. I can tell aircraft to fly a route, heading, radial, I can let them fly on their own nav, whatever....just as long as I get 3NM between them. An offset track seems fine to me. An opposite direction ofset is fine too. And I'll watch it on radar to make sure I get my radar sparation.
Having said all that, good practice - and a few years experience - tells me that having aeroplanes that will be close to the separation minimum on anything but assigned headings increases the chances of the bosses wanting to talk to me because there are too many variables that I cannot control in the equation.