I always find the Etihad onboard experience excellent. But the experience outside the cabin, that's a different matter. My most recent experience was the refund of an F-class award ticket due to equipment change to an aircraft without F-Cabin. I saved the miles over a longer period specifically to fly F so I didn't want to go the route of refunding the fare difference, rather cancelled the ticket altogether.
According to the call center agent an F ticket cancelled due to equipment change warrants a full refund.

The refund came after a while, but less than expected. Instead I found a cancellation fee entry in my account. I contacted Etihadhelp for help, and they suggested to help, after contacting them per email. Which I did.

What happened then is that the contact referred me to A who referred me to B who referred me to C and who referred me to D. In the process they sent me copies of my PNR which clearly indicated that I am eligible for a full refund. But the refund did not happen. At least so far. Maybe the miles will post, someday.

My recommendation with regards to Etihad Guest is to make sure that you take the straight path from booking with miles to taking the flight. The moment you interact with the Guest Support, things get much more complicated than you would expect, the processes take very long and may in fact lead to nowhere. Overall I find the experience of dealing with Etihad Guest more painful than it should be, which is a shame as Etihad's inflight product is very nice indeed.