It would actually make more sense just to charge the same fare for all three operators and remove any lower priced fares. If that naturally results in fewer Chiltern and LNR services so be it.In terms of revenue, it would make more sense to only have one London Northwestern Railway service between London and Birmingham but have three Avanti services on the same route per hour. This would encourage passengers to use the more expensive Avanti services.
Providing more Chiltern services running on diesel than are strictly necessary to handle the intermediate flows is complete folly until the route can be electrified.