Warlord, despite a certain amount perceived baggage with the name, is an evocative fantasy arch-type. Soldier is most definitely not. To begin with, it is far to modern sounding, which is why it is an option in d20 modern and Star Wars, but not D&D. Second, it is a bit bland and does not have as strong a connotation in a Fantasy setting as it does in more modern settings, and while one could make the same argument for the also bland Fighter, I would prefer a more fantasy or archaic sounding name. While WOTC has proven themselves capable of going overboard on the flowery names of late (coughDragon's Tail strikecough), I also dislike the bland and un-fantasy sounding tactician, expert, aristocrat, etc. If alternatives must be sought, I would be for the, IMHO, more appropriate Marshall, Champion, Captian, warrior, etc.