Ok, but that's not generally what sedition means

Irrespective of the undertones that you read in the word, that is what they are being judged for. It has a precise technical meaning in the law. And I’d like to know if there is any country whatsoever in which public uprising against the state from a government official, using public funds, and in the manner carried out by them in this case, is not prosecuted.

You have to take into account that this is not a military uprising of a few people, its a pacific protest from politicians who represent almost half of the Catalan votes.

There are plenty of examples where people have been pardoned in Spain for more ethically questionable reasons [1]. This, in contrast, is a clear case where it should be resolved politically, not through the legal system.

[1] https://civio.es/el-indultometro/2013/05/06/saenz/

The political pardon must come after the judicial trial, and comes from different, independent, branches of government.