Think about what you are saying.

Allegiant and Cape Air are not your typical airline models. Regionals are used to move traffic to a hub then to their connection. Both Allegiant and Cape Air are designed to move passengers to a specific destination and they maximize their revenue through diversifiying the O side of the equation and limiting the D side (whereas most airlines try to maximize both). Allegiant also gains 25% of it's revenue through incidentals, for a time a unique position, that is now trying to be emulated by all with their fees. Allegiant's primary competitor is the regional airline and AAA. Their direct flights are competing against two-leg flights or a 90min drive to the nearest hub of a major.

Any airline, regional or otherwise, can survive on it's own provided it is well managed and marketed. Regionals biggest problem is their lack of marketing and infrastructure as they rely on their major partners to do all the lifting here. This two items require A LOT of startup capital to invest and is a major hurdle to overcome.