For anyone who was wondering...
Some of us were wondering, how the showdown tiebreaker actually worked, given the fact the description leaves room for interpretation. So DodgyPutter, MioKontic and I, decided we'd go on a fun quest in the qualifier and test the system. What worried us was the "final showdown score" was not being fair, since people play the same 3-hole sets in completely different order, therefore someone, who gets a par 11 set as their last 3 holes would have a big advantage against someone, who gets a par 14...
What we discovered, with a bit of luck, "spying" on others and great help from sebicu and cusefan, who kindly shared their scorecards with us, was the following.
Although we all play hole sets in a different order, there's a unified pre-determined behind the scenes WGT scorecard, where every player's hole sets are arranged in the same order and that is used to break ties. When we play, we can't know, which hole set is being used as the last, 2nd to last or 3rd to last, by WGT. But it's the same order for everyone, no matter in what actual order we play them. We were able to establish the "correct" order for the countback for the qualifier, which was Erin hills as the opening set, Chambers bay as the middle one and Pebble beach as the final set of holes on the WGT showdown card. So, if one had the best score on Pebble, they would win the tiebreaker, even if they played it as their opening set of holes.
Anyway, fun times and mistery resolved. Seems the showdowns are at least fair in regards of people's scores being counted in the same order, even though the random conditions in every other aspect still make them a bit of a lottery 😉