You don't need to know all the answers to solve a problem. You just need to know where to look to find them.

Part of Emet's reasoning for selecting Hermes is based on this:
'That personal annoyance aside, Hermes' knowledge is undeniably impressive. Given that there are none among the Fourteen who specialize in the celestial, he would be a welcome addition.' (MSQ: Lives Apart)

It doesn't matter if there are people out there who happen to be experts in Celestial currents or Dynamis. None of them are on the Convocation and in charge of policy. This is the whole point of having an advisory council or cabinet. You could write a fanfic about how some recluse researcher broke into the Convocation proceedings, explained everything that was wrong with the Final Days and the solution before being arrested, and spared the Ancients the need for Sunder-Anchovy Pizza-Murder. But we have enough fanfics on these forums nowadays, and not enough actual validated lore.