Yes X is hesitant for fight and hence stays at class B but he actually does become stronger during the games. At the outset he's lacking basic abilities, like the dash, at the start of X1. It's also established that X gains new weapons and armour upgrades wheres as Zero only learns new techniques. X is building a new arsenal while Zero is simply honing his already established skills. Before X's upgrades he would likely be obliterated by Zero.
To properly answer the original question, despite adapting to become (the) strong(est?), I still don't think X would be classed as a war machine by the end, because he would still be capable of more than just fighting, and would choose another path as soon as peace is restored.