... what I also can't understand is why didn't they keep it all and do what Vivaldi has done? I mean they say these were rarely used features and were the cause of a lot of slowdowns in Presto, but yet Vivaldi has perfected it?
...
Opera was redesigned with a focus on appealing to new users who wanted a less complex browser, in order to try to grow market share and reduce costs. It was felt that the users who demanded deep settings and integrated feature capabilities were too small a market segment to devote significant resources toward for the development/maintenance costs involved. Vivaldi is taking a different path, focusing directly upon the users who want the deep settings and integrated features. Only time will tell which is the wiser choice of focus... perhaps both will be, each in its own particular arena.