This may just be my personal dislike of the guy showing, but I don't feel like Romulus adds anything to this War. I believe that Grue once said that a good Grail War is set up so that every aspect of a Servant's fluff gets used or countered in a believable manner.
Romulus has very few plot threads in this scenario, and those that he does have can be resolved depressingly quickly. Kintoki, on the other hand, has several long ones in the form of the ABB and the reaction one can expect to happen from the heir to the E88 summoning a famous Japanese figure as his Servant. In addition, Roma likely won't have any special interactions with any of the other Servants, save Iskandar, Nero, or Caesar, should they appear, while Kintoki is much less limited in terms of his potential interactions.