For clarity (ha ha) this is what the 261 reg says-
In order to ensure the effective application of this Regulation, the obligations that it creates should rest with the operating air carrier who performs or intends to perform a flight, whether with owned aircraft, under dry or wet lease, or on any other basis.
This was confirmed in a recent EUCJ case, Wirth v Thomson, which said-
In today’s judgment, the Court holds that an air company which decides to perform a particular flight, including fixing its itinerary, and, by so doing, offers to conclude a contract of air carriage with members of the public must be regarded as the operating air carrier. The adoption of such a decision means that that air company bears the responsibility for performing the flight, including, inter alia, any cancellation or significantly delayed time of arrival.
Accordingly, an air company, such as, in this case, Thomson Airways, which leases an aircraft, including its crew, under a wet lease to another air company, but does not bear the operational responsibility for the flight, cannot be regarded as the operating air carrier for the purposes of that regulation. It is irrelevant in that regard that the booking confirmation of the flight issued to passengers states that the flight is operated by the former air company.
https://curia.europa.eu/jcms/upload/...cp180100en.pdf
One area that does require amendment is where passengers book return flights to (say) USA via the BA website or App, get a long delay or cancellation on the return, which it turns out is on AA hardware, only to then find out they are not covered by the regs.
Sorry for thread drift but thought it may help.