100% agreed, a way to fully disable Aria is desperately needed. That it would not be possible as integrated too much into Opera is nonsense, it is just a question whether this is wanted or not.
One can disable the Aria background process for a while by manually editing the Preferences
file in profile data (while the browser is closed), search for "igpdmclhhlcpoindmhkhillbfhdgoegm":
key within extension block, and add "blacklist_state":1
to it, like the case for a number of hardcoded extension IDs, Opera obviously chose to prevent from running in this browser. However, the key gets removed in certain circumstances, probably on browser updates, not 100% sure yet.