Owe us? No. They really don't. However they might feel it's in their best interest, which it seems like they do, at least enough to give some sort of reason. Personally I am fine with their explanation. It at least enough for me to fill in the blanks. My take is this.
WoD was decided on late, only enough content was created for one year, they realized it sucked and subs were lost in part to that reason, decided to abandon ship not even finishing every thing planned on in WoD in order to finish up Legion. Hoping to capitalize off the natural uptick that comes with new xpacs they plan to recapture some of those lost subs with what is hopefully an expac that is superior to Legion.
Simplified perhaps, I bet there are a lot of moving parts and nuances in all this. And of course I could just be wrong.
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This is what I did. Just stopped playing till they announced legion, then came back to prepare a bit. That being said, I can both stop giving them money, play other stuff and be interested in what they have to say in regards to these matters. Even if ultimately it doesn't affect my personal choice as to whether I will play and pay or not.