Fortunately the more historically valid characters are interesting as people try making moral/self-interested/honorable decisions within a 13th Century Christian context. Those three goals really are the stars by which each character attempts to triangulate their decisions. By moral I mean following the teachings of Christian and by honorable I mean living up to the Germanic warrior code. Self-interested is rather self-explanatory, but there are political and economic versions of it.
The entire Crusade is famously derailed by the need to pay the merchants of Venice for use of their ships, getting side tracked into fighting Venice’s battles against other Christians for them. Not a single Muslim is harmed in the prosecution of this Crusade, but Constantinople is sacked.
So if you can put up with the main character long enough, the book pays off as you get more interested in everyone else.