I think watching the pro-tour to decide what deck is best for your local game store is a lot like watching the Superbowl to decide what plays you should try during a pick-up game with friends. The Magic pro-tour is a very meta-specific event, and for this one the "talk of the town" was the Saheli Copy Cat deck (
https://www.mtgsalvation.com/forums/the-game/modern/deck-creation-modern/769336-jeskai-copycat-saheeli-felidar). Everything I've read has said the pro's all used that as their yard-stick. If a deck could beat it regularly, they'd keep testing it, and if not, they'd try something else. Turns out, Mardu vehicles is very good against Copy-Cat, as well as against a lot of other decks. Therefore, it did great overall.
Now, if something like U/B control is very popular at your LGS, then blindly playing Vehicles is probably a bad idea, since all the removal in U/B control makes it a very hard matchup for Vehicles. However, at the pro-tour, nobody played U/B control because it isn't great against Copy Cat, and anyone who did play it was weeded out by all the Copy Cat players.
As for your original question ladof, more often than not the top 8 usually
boil down to 2-4 dominant decks that usually reflect the meta of the event itself. Whether it's Mardu Vehicles here, Bant CoCo, Green/White Tokens, or Caw Blade. The decks that are best for that particular event will float to the top.
Another great example is the Modern GP in Dallas 2016. I know GP's are very different than the pro tour, and I also know Modern is VERY different than standard, but
Skred Red won that GP...
Skred has been a deck forever, and NOBODY would call it a tier one deck. However, it has particularly good matchups against Dredge and Infect (pre-bannings), which were the decks to beat at that Event. Since
Skred made easy work of those decks, by the time he made it to day 2, the field was mostly Dredge and Infect, so he came out on top.
I think too often we
jump to the idea that if the pro's play it, it's the best, when really it's more like, "if the pro's play it, it's a good deck to play against other pros"