A few observations on Phase 1:
Winners
Kartana - Fourth highest in usage and a very impressive 72.7% winrate speaks for itself; Kartana's found its way onto a variety of teams and thrived so far. This makes some sense as a response to some of the surging bulky Normal-types, and its sets have changed to reflect that - Fightinium, Sub, and bulky Tailwind sets are all proving pretty successful. It should be interesting to see how this changes for Phase 2, since it's never had this much usage before.
Chansey - Speaking of something that hasn't had this much usage before, 6 uses may not seem like a lot but when Chansey's record was 5-1, it's pretty notable. One way or another, this Pokemon inspires strong opinions from pretty much everyone, as its staggering bulk and hugely beneficial support movepool can make it a huge pain to take down. Porygon2, another bulky Normal-type, has also had a decent tour thus far, though 3-1 isn't really enough data to say for sure yet.
Assault Vest Victini - The set that originally got Victini ranked, its Choice Scarf Final Gambit set, hasn't shown up yet, but other Victini sets are absolutely thriving, with a 4-1 record and the only loss recorded inside of a mirror. The biggest noteworthy change has been the appearance of Incinerate Assault Vest Victini, enabling it to support its team through *double* berry removal. It might seem strange that a set which completely folds to Incineroar is showing such success, but outside of Incineroar this Victini does incredibly well against the meta right now.
Losers
Kyurem-B - Every tour up until now, Kyurem-B's performed up to expectations, but a 1-6 start is very unconvincing. Despite its versatility and access to coverage that hits most of the metagame, Kyurem-B can't seem to pull through when it counts. Some of this can be explained by the winners listed above, as well as by Mega Metagross having the most usage and most wins out of every Mega, surpassing even Gengar.
Diancie - The Diamond Storm pixie can't seem to propel its team to victory, going winless across three uses in its base form and two as a Mega. It's difficult to say for sure what's caused it to struggle so much, but notably Trick Room-based teams have been quite rare, and the teamstyle where Diancie has shown the most success - Mega Camerupt TR, was entirely absent.
Power Rankers - Once again the preseason power rankings have been shown to be pretty irrelevant; with no 4-0 players, the best record is shared by players ranked 3, 7, 8, and 10. Four games isn't enough to say for sure who will have standout tours, but the field is clearly quite even and remains difficult to predict.