I never claimed anything was int he TOS so please don't attempt to put words in my mouth. If you are willing to invest 500mil into a single item you definitely do your research before purchasing that item. So yes, if you did purchase a duped item it is on you.
With that said the real issue here is the duping of gold. Which I am pretty sure this fix isn't going to affect at all. Account rollbacks should also be limited to 100mil gold restoration or none at all.