What happened to the good Second Foundation? And what is Speaker Delarmi's deal?

In Second Foundation, the book depicts the Second Foundationers as these strategic yet vulnerable people that are doing their best to keep Seldon's dream alive. They are idealists. They sacredly hold the dream that one day there will be a new peaceful Galactic Empire worked out by mathematics, despite The Mule.

So, how can someone like Delarmi from Foundation's Edge be allowed to rise to the ranks of Speaker? Had the Second Foundation become corrupt? Are Second Foundationers largely just petty bureaucrats who bicker internally except for a dwindling few who believe in The Plan? Honestly, I've read Edge many times and it's always wild to read the chapters where Gendibal is trying to warn everyone about Gaia. The majority of the Second Foundationers are more interested in putting him in jail!

Is there something about Delarmi's character that's salvageable? What did Asimov intend to show by having the Second Foundation be much worse than originally presented?