So what I'm trying to understand is how you and all others who accept only a "single variable comparison" think it is fair to mount the same arm and cartridge on two different tables and then judge which table is best? Yes this may tell you which table you preferred within that particular "system". But in my mind it will not necessarily tell you that your choice will be preferred in all systems, i.e. that it is the best of the two tables. If one size fitted all, this would be a far simpler hobby.
after first acknowledging there is no real ultimate truth of 'what's best' when comparing tt's, i think one can form useful conclusions with reasonable efforts. particularly when you own 2 or 3 tt's over a period of time amd move arms and cartridges between them. characterisitics do emmerge. preferences get established. if that preference holds in multiple situations it gains in credibility.
it helps to have 2 of the same cartridges, or two of the same arms, or even a phono stage with 2 inputs. this allows speedy 'single varible comparison'.
but for me it's the months of listening to tt's side by side which allow a real sense of what is what. quick looks are useful but less valuable for me.
as far as 'system' synergy; i suppose there are amp/speaker/room combinations which may favor one vinyl front end over another. maybe tubes and horns may invite idlers and Koetsu's, as an example......but at the top of the vinyl food chain i don't see much of that approach. vinyl gear that aspires to be SOTA are typically all around performers and not limited to one system character.
at the end of the day colorations will always get in the way of the musical message.