If Starlink becomes common enough on flights, I absolutely believe it will be a competitive disadvantage.
Frequent flyers choose their airlines for a lot of reasons - which airline has the most direct flights from their city, who has the best frequent flyer program, etc. The latency of the Internet is seldom a factor or the difference between 10Mbps and 50Mbps.
Non frequent flyers just buy the cheapest flights. The major three airlines make money off of business travelers, business and first class flights and credit cards.