That would seem to be standard procedure.
Quote: "We must stress that ABTA doesn’t award compensation or make a decision on your case".
Source:
https://www.abta.com/help-and-complaints/customer-support/resolving-disputes
If you're sure you've got a good case, fork out the £108 fee to go to independent arbitration. If you win, you'll get that back plus appropriate compensation. If you lose, you'll have to pay a further £108. (I've assumed that your claim isn't for more than £7500).