You're judging it against what, exactly?
At less than 15 years after Japan had been totally devastated (much more so than Germany, for example) I think it was an extraordinary statement of ambition and intent and an indication of what was to come.
Whaoh...you judged it first :
A little sports car from humble origins, aiming to punch above its weight .....
key words "above it's weight" ! So what were you comparing it too ? There was nothing in the JDM so you're talking foreign makes...MGA, MG Midget ? But be careful, you stated ABOVE it's weight which I can accept for the SPL and SRL311s but at less than 300x produced (+500 with the SPL213 ?), this was a loss-leader surely, to prove to the JDM and elsewhere that Nissan was big enough to make 'luxury items, non-practical cars' and for that, I give them enormous respect especially only several years since they were constructing imported Austin kits.
Yes, it was an ambitous step forward but a modest one with the SP212. The big step came with the SP310, a year before the MGB roadster.
Humble origins ?
'Nissan' was the first automobile manufacturer, made Japan's first car and grew to be the biggest JDM automobile manufacturer at the time of the Fairladys' 'coming out'.
If you mean orginated from the Gorham, Dat or Lila then yes, agreed but then Jaguars too came from humble sidecar bodies but only 10 years after our favouraite marque.