The thing is, Jackson already fills quite well the role you would think a guy like Rhodes can fill. Jackson is a good reciever out of the backfield, and is likely shiftier and quicker than Rhodes, at this point. Therefore, Taylor would have been a better back for the Bills, because he could be our Marshawn at the beginning of the year, when Lynch is in street clothes.
Another way to look at it, is none of us seriously thought we would sign Taylor...the thought of him signing here to be a third running back immediately struck us (or most of us) as unrealistic. But with Rhodes, that doesn't seem unrealistic in the least, as thats what he's been the last couple of years.
I agree there are SOME things Rhodes can do better than Taylor, mainly catching the ball. But if we're talking overall backs, there's no conversation, IMO.