Difference being of course that when you go to the theatre, concert or similar for entertainment you know what you're going to get and you know who's playing, you can check reviews and so on. Fact is as well that virtually nobody goes go big concerts or events every single week. Of course for home games that's mitigated by a season ticket (probably makes it about £14 a game at the cheapest).
If football is an entertainment industry as you describe then that has to justify the cost and it has to be, well, entertaining (and I don't mean always winning). It very often is not.
In my opinion, given the 'match day experience' and entertainment on show there's no justification for any Championship game to cost over £20 for an adult.