Judging a good deal is all about perspective. That’s especially true for budget airline Frontier’s initial public offering. The U.S. carrier is seeking a $4.5 billion enterprise value, putting its relative valuation higher than big peers like American Airlines. A premium may be warranted. But American is also worth more than before the pandemic. That tailwind will disappear.

Like other air carriers, Frontier’s business took a hit in the past year as travel halted. Revenue halved in 2020 compared to the previous year, and EBITDA swung to a loss. But in some respects, Frontier is stronger than larger carriers like American. Low-cost airlines have been ramping up in the United States, and Frontier was growing at a faster clip before the pandemic: Revenue was up 16% in 2019, while American’s revenue was roughly flat.

Its costs are also more manageable. Expenses per available seat mile, the industry metric for operating costs divided by seats, then by number of miles traveled, jumped only a fifth at Frontier in 2020 versus a third at American. That suggests that it is better situated to managing its costs as revenue declines, helping it to weather a prolonged recovery from Covid-19. Frontier’s targeted enterprise value of 3.6 times revenue, in line with Southwest Airlines but a 50% premium to American and Delta Air Lines, could be justifiable in that light.

But that assumes American is fairly priced, which probably isn’t the case. Though its shares are still more than 20% below their pre-pandemic high, both the company’s market value and its enterprise value are significantly higher. That’s because American has been issuing equity, but spending cash quickly. At the same time, the market isn’t punishing the company for taking on more debt. In fact, while an individual share is worth less, the market value overall is almost 15% higher than February last year.

That means a reckoning for American’s value, and, by association, Frontier, if airlines’ losses continue. There are other operational risks. International travel may not return soon, and business travel may never get to levels it reached before Covid-19 took hold. Frontier is getting a lift from puffed-up peers, but the air is likely to thin.