No, multiple PSRs do not necessarily mean that you have improved track accuracy. For that to happen, one has to have track to track correlation, with some kind of smoothing and filtering. Mathematically it's not trivial. So, what most air surveillance systems do is pick the tracking source in which they have the greatest confidence and ignore or suppress the other inputs.
Also, most PSRs scan in az, but not in el. IOW, we don't frigging know how high you are, hence Mode C. Military surveillance systems will use a combination of search and height finder radars to develop a track that is coherent in az and el.
Phased array radars of course can do it all, but the el scan tends to be very duty cycle intensive. IOW, you can lose the track while you're farting around trying to see where the target is in el.