MOL clearly wants to use this as a signal to other airports thinking about airport charge increases, planned or unplanned. That said, there is clearly no shortage of other airlines happy to jump on a busy route to pick up the slack left behind - the route capacity will drop by half (14 ATR72 against 10 738) so Arran should do well if they get the fares right. £19.99 for starters sounds great, especially as most of the Ryanair passengers for the first two weeks will have the option of getting 250 euro compensation and a cheap ticket on Arran or else staying with Ryanair to fly to Bristol and get the bus to Cardiff.
Arran will also get in just in time for the FA Cup Final and the rugby final, so should clean upon these weekends.