Read the Word bearers Omnibus its one of the better 40k novels in my opinion. I would say it’s not just the Word Bearers versatility that’s underrated, but also the pseudo meritocracy that their legion has By allowing the most competent and vicious members to rise through the ranks giving them solid leadership vs say the night lords in their trilogy books who are led by a daemon thats just using them as pawns which leads to the war bands downfall.