Can you explain this a bit further? I'm not saying you're wrong, but I always thought that utilizing the 3-4 as the base defense gave the DC an advantage in terms of versatility. Linebackers that can either rush the passer, play the run, or drop into coverage. That is, of course, if the DC had the proper personnel.
The Bills were clearly lacking a true NT for the scheme, and many have contended that Preston Brown was playing out of position as a 3-4 ILB. Also, not having competent safeties hurt us, but that would adversely impact any defense regardless of scheme.
Not trying to defend Rex's 3-4 at all, but wondering why you think the scheme itself is somewhat antiquated.