There has been a poll to decide whether to move from PO or not. An increased majority was in favor, so it passed. Beside the irregularities in banlists, the website failed to upgrade normally, and the environment was less user-friendly, thus increasing the likelihood of the change.
I will repeat some parts since they might not have been clear.
Dennis himself proposed the ban. He was fine with where his team was on the ladder, however baton pass teams became too much of an annoyance that everyone had to bring the musceteers in their teams to counter them (and other options ofc but those were everywhere). Forcing the metagame to shift just to counter specific pokemon or moves is unhealthy for the game, as it does not allow other strategies to appear or work properly.
Shadow Tag is much superior to Arena Trap, and as I said, it's not Wobbufett we worry about, since it's in the same league as Duggy. Gothitelle was the mere reason ultimate trapping was stopped, and Wobba was the collateral damage. They could enforce a complex ban of Shadow Tag + Trick but they chose to ban the ability whatsoever. It works for the metagame since it's easy to adapt.
Now, since this topic discusses mainly current tier changes, with bans, ups and downs etc, I believe the Shadow Tag discussion needs not continue. If you like, we can create a new thread about this, where we can discuss further, with more detail and probably calcs. Discussions about shaping the metagame includes the removal of bans due to how fluid the competitive scene becomes after each major game release, which is what I'm expecting come November. Yet not here, as multiple discussions will derail the topic and we'll be forced into the limbo of off-topic-ness.
Wait till September 30th for (hopefully) new movements inside the tiers.