I always liked the Diana, true it had its downsides, but I thought it made some sense to base it on the M1, after all, with the replacement of the M1 with the M1A1, its not unreasonable that the old M1's was diverted to produce it with a simple turret replacement, cheaper than buying a whole new vehicle.
However, I agree, its not the best option despite the fondness I have for it. Honestly, I think a gun/missile system based on the Brad would make a lot more sense for various reasons - hence the M6 Linebacker. One of the things that the procurement process got right for once.