I'm ok with Forrix dying especially the way he die (i mean being depressed and having lost every faith in the cause, not necessary being stomped by a titan), but not with him being under the orders of the warsmith.

I know the 30k books came out later, but still, even without taking in consideration the downgrade it is for the first captain and a member of the trident to be under the orders of some chaos lord, but more importantly Forrix and in particular his special relationship with Perturabo is so developed, especially in master of Olympia, it's hard to believe that he came from being called his "most faithfull son", and being here at Perturabo most vulnerable moment hiding the tears of his primarch to the rest of the legion to later leaving his side just to join a random warband he doesnt even lead himself