Delta Air Lines is the country's most profitable airline, posting nearly $14.7 billion in profits over the past five years, almost double its nearest rival. CEO Ed Bastian, now marking his decade at the helm, credits a strategy of courting affluent travelers willing to pay premium fares rather than chasing price shoppers. That bet has paid off even as Spirit Airlines shut down and jet fuel costs climbed roughly 50 percent.

Berkshire Hathaway's recent move to take a more than 6 percent stake in Delta signals Wall Street's confidence in the carrier. SkyMiles alone is valued near $32 billion, roughly two-thirds of Delta's $50 billion market cap. United Airlines, led by CEO Scott Kirby who proposed a merger with American Airlines, is chasing the same premium customer base Delta built over two decades.

Bastian insists Delta will make incremental tweaks rather than radical moves. Spirit's collapse proves that no strategy holds forever. Flight disruptions, union tensions among pilots, and growing labor organizing efforts at Delta mean the loyalty machine Bastian built faces real headwinds ahead.