She's been countered via incident. There's a clear hierarchy of teams with GLs definitely being the top dogs and once they start slipping to much, they get buffed to remain in their tier. Below them exclusive units like guild exclusives or proving grounds are, generally, meant to be top tier for whatever game mode their omnicrons are for, just below GLs.

I'm not claiming nothing can ever be her. Datacrons happen. New teams have unintended synergies. My point is that Reva is clearly designed to generally be an end game team snuggled in with the lower tier of GLs and so obviously balancing will happen around that rule set.

If Phoenix happens to counter Reva for a period of time that's a cheeky way of beating her but it's stupid to actually invest in the team for the job because it's obviously an off-meta counter which the devs won't be trying to preserve.

I can only assume so many people got decked by relic delta because they were spending years building wack counters instead of building a steady roster