I guess what I find issue with is any card that contributes to invalidating a slot/section by just being the best choice in that position regardless of synergy considerations. That's maybe me decrying higher power levels, but not exactly what I mean.
For example, I don't want to play the rockstar 1 mana cantrips like
ponder in my GY format because they contribute to invalidating other draw mechanisms I have in my cube that support my design goals (
cathartic reunion,
careful study, flashback spells as card advantage, etc). Even if the play pattern is "totally fine", it decays the usefulness of slots around a card when it's a standout rockstar, especially more niche synergy picks that suddenly look less attractive because XYZ generic powerful thing can be maindecked instead.
("why run this Think Twice for it's #synergy with my Careful Study? I can just run a way better cantrip and forget both those other cards!")
My personal opinion for your format
@inscho is that Tracker reduces the viability of things like
turntimber sower,
loaming shaman, and
world shaper because if I draft tracker it becomes a default slot in my deckbuilding, so might lead to me leaving out the more interesting stuff for the raw power. I become less incentivized to chase a GY combo if I can just take the path of "play a normal game of magic and I get this monster body + card draw engine".
it is just one card so maybe it's not all that, but that's the angle I take, and something I am continuous looking out for in my environment.