That's life in the commercial world. A converse view is that American, BA et al have spent decades building up commercial links between London and New York, and now upstart carriers come along and try to cream off the best of the traffic, and get annoyed if the established operators make any move to compete.
British Airways ....... still being able to retain a monopoly of slots at LHR
Do you not remember that Bermuda, and Bermuda 2, were an AGREEMENT between the UK and US governments. The way it was portrayed latterly was that it was something unilaterally imposed by the UK authorities. One of the aspects of the agreement was that for many years after the agreement there were two US airlines (Pan Am and TWA) and only one UK airline (BA) operating to the US from Heathrow.
And if you think BA have (or even had) a monopoly of Heathrow slots I can only presume you don't come through Heathrow a lot.