Well, that's true (in part, you have tons of ournaments in TTS or BCP), but you don't need so much data when changes are pretty straightforward.
We all know the armies that are on top of meta and how oppressive are to play against (KO, Seraphon, Tzeentch, SC) and We know wich armies are on the bottom of the barrell.
Second thing is easy fixable and they seem to be working on that on BR or Celestial Tomes (well, sometimes getting a good success like Nurgle in WotE, Throggots or IDK, sometimes being terrible like S2D in BR), but to clean up the meta you need those balance changes.