How is it a pyramid scheme exactly?
A pyramid scheme is defined as "an unsustainable business model that involves promising participants payment or services, primarily for enrolling other people into the scheme, rather than supplying any real investment or sale of or services to the public" (source: Wikipedia.)
The fact is, regional airlines exist as a legitimate business model, much in the same way a general contractor passes work down to subcontractors. Mainline will only continue to use regional subcontractors as long as it makes financial sense to do so.
Mainline carriers are bound to their customers, who vote for which airline will succeed using their wallets. Regional carriers are bound to their mainline partners, who vote for which airline will succeed with fee for departure contracts.
Given that most regional carriers have roughly similar fleets and pay the same for fuel, the only major cost variable which can be controlled is employee pay. This places regional carriers like Envoy at a serious disadvantage due to their very senior pilot group. Furthermore, most of the FFD carriers today are struggling with ever thinner margins, despite success at mainline. Finally, mainline carriers are consolidating their regional feeds by trading out smaller 50 seat jets for larger ones (but not one for one), so much of the shrinking we are seeing at the regional level is not really as worrisome to mainline as we may suppose. This is more true for AA/US because there will be even more consolidation due to the merger. When Envoy voted "no" they chose which airline mainline would be "rightsizing."