Y'know, one thing often forgotten about in the debate over “Was Eltoshan stupid or what?” is the context.
Everyone in Gen 1 was SOL by design.
Seriously. Let’s say Eldigan fails to save Chagall at the end of Chapter 2 and gets declared King of Agustria. Think Grannvale is just going to back off and let him be king? Yeah, no.
Best-case scenario is, Eldigan stays king for a couple of years until Arvis takes over and then he goes down around the same time Leonster and Silesse fall. Worst-case scenario is that King Eldy very quickly grows tires of Grannvale being all up in his business, has a falling-out with Sigurd, and either dies in battle or gets executed. So, pretty much what happened anyway.
All his options were bad ones. Agreeing to have Chagall deposed would have compromised his own high-flown ideals and not left him any better off in a practical sense, because really the best he could hope for was a few years of being Grannvale’s puppet. No thanks.