I think what shrang is saying is that the checks and counters to these Pokemon are sub-par because they over-centralize so much; for example, Arceus-Rock would be way inferior to Arceus-Water or Arceus-Electric in a meta without Ho-Oh (no, I'm not suggesting we ban Ho-Oh [not even mad if we do tho]). To quote the analysis:
That's what over-centralization does: it makes people use less effective or niche Pokemon to beat a certain powerful threat. However, Shadow Tag over-centralizes less, or at least not more, than some powerful Pokemon; Ghost-types cannot be trapped, Dark-types (see: Pursuit) beat all the Shadow Tag users, and there are many Pokemon the Shadow Tag users cannot trap. On offense, many Pokemon are too powerful for Mega-Gengar and Gothitelle (and maybe Wobbuffet) to switch into, like Lustrous Orb Palkia, Kyogre, Yveltal, Mewtwo, Ho-Oh, offensive Arceus forms, and more; on stall, many Pokemon, like Blissey, carry Shed Shell (I concede that this is an example of over-centralization to a degree), or cannot be trapped by certain Pokemon; for example, Gothitelle cannot trap Heal Block Klefki. Balance usually carries few Pokemon that can be trapped by Mega-Gengar, Klefki, or Wobbuffet, and brings a Pursuit-trapper if they do.
"Shadow Tag is uncompetitive!" is another argument I would like to address. The definition of uncompetitive is listed below:
In my opinion, Shadow Tag does not take away a significant amount of autonomy-at least, not enough for it to be banned. You always have control; the moves you can choose, and sets you can run, are different choices the player can make that affect the outcome. True, Gothitelle can trap and set up on any Pokemon that cannot significantly harm it; however, that's the player's fault for not preparing for it. In addition, like any other threat, Shadow Tag can be played around with clever double switches, U-turn, Volt Switch, or Baton Pass, or other ways to beat it on individual Pokemon. Shadow Tag users are just new threats that must be prepared for differently; instead of bringing one designated counter, each Pokemon must be equipped to check it (or have a Pursuit trapper, the option I like less). This is a change, but not necessary a negative one; the metagame can and will adapt.
Finally, I'd like to talk about Shadow Tag in regards to Ubers philosophy. According to bojangles, the BW Ubers tier leader, Ubers is "the metagame with the least amount of bans possible." That alone tells us that we should not ban Shadow Tag unless it is absolutely necessary; as you can see from my paragraph above, I don't believe it is. Personally, I see no way Shadow Tag violates Ubers philosophy; sure, it causes reliance on team matchup to a degree, but so do many things. As I said earlier, it's a player's fault for not being prepared for a threat, and Shadow Tag, while very effective, is still just another threat. Team matchup is inherent in Pokemon; if your team is all grounded, relatively frail threats, then you are going to get torn apart by Sticky Web. Without wallbreakers / stallbreakers, lures, or powerful setup sweepers, Stall tears you apart; see where I'm going with this?
In conclusion, I believe that Shadow Tag should not be banned. Thank you!
tl;dr read the thing
Gonna cut you off right here and ask you to tell us, specifically, how one prepares for or adapts to Shadow Tag. Saying "it must be prepared for differently" is a blanket statement and telling players that its their fault for not preparing for it is a "git gud" argument (which was not acceptable for the previous test and is not acceptable now) unless backed up with specific examples.
(Also as an aside, the statement that Gothitelle can't trap Heal Block Klefki is false, orch posted a set literally just last page that is capable of doing so.)
Expulso, are there any sets that you can post that are ways to prepare for Shadow Tag users?
EDIT: No longer relevant due to Ninja Brian above me.