Well i would have thought any game develoepers would put fixing bugs at the top of any schedule instead of adding more buggy content. If you suggest they should add content before fixing bugs then your playing the correct game.
Personally, I think they need to do both, fix bugs and add new content. To this end, I believe that every publish has had bug fixes completed that were not in the original publish notes, and some that are just not even in the final notes.
Additionally, I suspect that bug fixing 15+ year old code with 70+ publishes and major additions to the game has got to be rather tricky.
And are you really suggesting that zero new content be added until all bugs are fixed. That, would create a much steeper decline in UO subscriptions, IMHO.
Not cheerleading, as I too want as many bugs squashed as can be squashed, but to do so without adding new content, which given the age and complexity of the code involved is sure to create additional issues, is mere fantasy, and will drive more customers away.
The dev team needs to do both.