I can see your point and I don't want to turn this into a "Zero vs stay/night"-thread but what I meant is that most of the cast in Zero doesn't undergo character development and is pretty static for the most part. For example: Tokiomi is basically a guy who already chose his path in life, so we don't get to see him struggle that much between being a parent and a magus while Rin's entire character arc in F/SN revolves around her struggling between being a mage and a "human". And it's not just Rin or Tokiomi, I think the same about most of the cast except Kiritsugu, Kotomine and Waver. And then again, Kiritsugu's character arc is way less interesting to me than Shirou's as we basically know already that the "Hero of Justice" ideal doesn't work the way Kiritsugu wants.
But I'm not a big fan of Urobuchi's stuff itself, so maybe I just prefer Nasu's approach.
For me it's the characters and the world building. Especially Emiya Shirou is a very interesting character to me and his thoughts and relationships with other characters make him a deep character imo. Most VNs basically have a main character who you should just self-insert into but you can't really self-insert into Shirou because of his state of mind. He is broken and mentally ill person and you have to understand him by choosing not the thing you would do, but making the choices HE would do.
That's at least how I think about F/SN and it's definitely not for everyone, but I would never call it bad. Sure, there are definitely some things that could be done better but you can say that about everything lol.