A Captain Sulu show would have been no more successful than any other random crew on a random ship. The core fans are not the people that need to be watching week in, week out. It's Joe and Jane Public, who are unlikely to be any more interested interested in a show about Sulu than they are about anything else.
Could a show about Sulu have worked? Sure, but it's no more or less likely to be successful than any other concept.
The new movie was successful because it catered to non fans and casual viewers. It's no more complex than that.