People - I'm not sure my previous message was sufficiently clear.
AENA is a Spanish public body that is part of the Spanish Govt and whose sole duty is towards the Spanish Govt. If the prime minister of Spain tells AENA to raise the landing fees at Spanish airports and pass some of the extra cash to the Govt, then AENA will likely do so (a refusal will likely mean the head of AENA needs to find a new job quickly).
AENA doesn't give a toss what Luton council wants or says. Anything AENA does outside Spanish territory is purely to make money from airport management fees. AENA know that Heathrow and Gatwick are both full and that Luton has no more space for overnighting aircraft - i.e. demand for access to Luton far exceeds supply. Heathrow, Gatwick and City are full at peak times. Typically in a free market when demand exceeds supply, the price of the product (e.g. landing fees) will increase until demand reduces slightly to equal supply.
If AENA ends up running Luton, they will manage it in a way to maximise the profit - i.e. maximum fees, minimum expenditure on the airport. Spanish Govt owned AENA does not care about whether something is in the interests of a passenger who is not resident in Spain and does not have a vote in Spanish elections.
AXA is investing money from places like pension funds and insurance premiums into Luton. AXA cares only about good stable long term returns for the money it invests. If the returns AXA provides are below average, the trustees of a pension fund are likely to fire AXA and replace them with a different money manager. AXA is not interested in the interests of Luton's passengers.
There's plenty good about a private company running airport infrastructure when there is genuine competition with other nearby airports - much benefit has come from the UK's utilities and infrastructure being privatised and becoming much more efficient instead of the bloated inefficient monsters they were while in Govt hands.
Maybe replacing the management by Abertis with that of AENA / AXA will bring renewed vigour and efficiency. It will not however turn Luton into a charity.