This is really a faulty point... As RJ operations grow at the expense of mainline, the time required for a pilot to move up from regionals to majors also increases. The senior pilots at the regionals aren't really any less experienced, in the grand scheme of things, than the junior pilots at the majors. "As the proliferation of these aircraft continues," the major carriers will have fewer job openings, so they will higher fewer pilots, and pilots will accrue more seniority at the regional carriers flying RJs. At least a Comair captain has been flying RJs for a while before he becomes captain... it's entirely conceivable that a Delta pilot can step into the cockpit of a particular model as a captain even having never flown it before.