If that is close to explicitly as you have stated then either 1) The senior bank people you talked to are lying to you 2) the senior bank people you talked to really don't know anything about PSD2 3) They mistated to you how PSD2 changes will affect this 4) You misunderstood what they mentioned about PSD2 changes.
If a bank mentions in its clauses as per PSD2, that only authorized persons/firms are use an API and their acccess, they are authorized to negate any liability if it was given/accessed by an unauthorized party. Banks are required to make API's available (not same as accessible) to any SaaS or other developer as long as it is authorized by the bank.
Rather than relying on hearsay or in conversation on crucial regulatory changes , might I suggest this: https://www.createspace.com/5772402
