The grounds for granting the review specifically state that it is
not based on usual judicial review (which would have failed) but because the prorogation was intended to "stymie parliamentary scrutiny of the executive". It has good legal lineage.
ETA: The English courts decision has been released in full (24 pages,
link). That court ruled that the prorogation was "non justiciable", i.e. outside the purview of the courts. Basically this placed the matter in the separation of power arena, political decisions or "matters of high policy".
The Scottish court actually agreed with this,
but decided that
this prorogation was an attempt to frustrate parliamentary scrutiny of the executive.
ETA2: Here's the interesting bit in the Scottish decision: