'They really don't want sellers picking and choosing which of the available postage methods they are willing to use - to be fair, that would rather drag us back to the pre-SD days.'

It would be a poor state of affairs if private sellers had no choice at all over postage methods, although eBay are doing their best to restrict those choices.  At least it's possible to opt out of InPost, and whichever courier you can't/don't want to use - and there are still some Custom postage options available. Unfortunately, the whole postage situation now just feels like a bit of a hotchpotch. 

I wouldn't need dragging back to pre-SD days... I'd go willingly.