What super radar? LolOne thing you can do with a 25-30k ton ship that you can't do with a pair of 12-15k ships is house the same super-radar.
Note that in my conception such a heavy cruiser would fulfil a different role from the 055s. Instead of being oriented to AAW (or at best jack-of-all-trades) like 055 and similar workhorses, the cruiser brings the big radar to be employed by the entire battle fleet, whilst its own munitions are focused on delivering an offensive punch through a heavy load of land-attack missiles and naval gunfire support.
And if railguns turn out to be at all practical, they will be easiest to field (and have the greatest potential) when fitted to a large hull with power to spare.
Radars no matter how powerful are still limited by the earth's curvature. Like I said in my earlier post any specific sensor or weapon systems you can fit in a 30k ton warship you can probably fit in one at 15k including rail guns. It's about power manegement.
Also PLAN's theatre of operations is primarily in the pacific for the foreseeable future. A 30k battle cruiser in very very limited numbers would end up being a dock queen and actually becomes a liability in times of a major conflict.