Dont talk shit.
Formations are fluid and very different roles between the three mids.
Saying 'midfield trio' means absolutely nothing.
It means, that the 3 need to play close to each other in order to control the midfield, that's how the system is supposed to operate when there is pressure involved. Maybe watch a bit of Xavi, Busi, Iniesta, and see the distance between them or Messi (when he participated to midfield).
Under Koeman, it is Busi (lol) vs 2-3 while the other 2 are sitting higher waiting for some magic passes that rarely come. I've seen this far too much already. Koeman is very much a conservative manager. He will have a basic setup, quite stiff (reminds me of EV), and bank it on player quality to carry him through. Not really how modern football goes these days. Unless you have an elite side in place, in which case any decent manager will do.
The midfield trio works like a sponge. When the passing lanes are more generous, the sponge expands and lets the ball do the work. When there is pressure on the ball carrier and no comfortable pass options in sight, the sponge contracts as to present ways out and beat the press in close compartments. Then as the pressure is relieved, expands again, pretty quickly. With Koeman, it's expanded all the time. There's not much tactical nous at display here. Don't kid yourself.
Even a Championship team in England with legs and stamina to carry all game could put this Koeman Barca under heavy stress. And don't tell me they have better players lol.