Thanks for trying it out! Schema.org validator tends to focus on Google supported structured data and can lag behind the actual vocabulary spec. So the tool validate against the full schema.org definition - things like deprecated/superseded properties (e.g. founders > founder), type mismatches, and empty required fields that their tool often lets slide.
Every time I worked on JSON-LD I ended up with three tabs open: the Schema.org validator to check it's valid, the Schema.org docs to figure out what properties exist on a type, and my own JSON-LD somewhere in the middle. The validator doesn't help you discover, and the docs don't help you validate.
SchemaLD (https://schemald.com) puts both in one place. Paste a URL, it pulls the JSON-LD, validates it, and gives you an inspector where you can click any node to see every available property with its description. Edits update the JSON live.
Free, no signup. Would love feedback — particularly on which schemas it handles badly so I can fix them.