operaoperandi, avi, see Chrome, Firefox and Opera for comparison (OS X Yosemite):
I think it is indeed an antipattern, even though window controls on OS X are generally on left side. I think we should rather follow Firefox / Chrome in this matter, not Safari that has even smaller market share than Opera. Moving from Chrome or Firefox to Opera is literally impossible on OS X because it is nearly impossible to get used to the weird UI, especially if you're using two browsers (FF + Opera or Chrome + Opera, what I do).
If you think the closing symbol on tab on the left side is alright - I'm fine with that, but I still think it hurts Opera a lot. Can I change it somehow? Maybe there's some plugin that will move the X symbol to the right side? It just makes no sense to have it on the left side, at all.