Even with the ad blocker being a feature in opera out of the box?
They were trying to show that opera can achieve better battery performance based on it's features and optimizations. Does that not include the ad-blocker?
I just loaded up MSN.com and scrolled down the page. I count 3 ads total: one gigantic banner at the very top of the page before all of the content, and two smaller panners that pop into place as you scroll. These are served by AdChoices. When I turn my ad blocker back on, these all disappear, and the site loads much faster.
I think if Microsoft were to release a default ad-blocker, they would need to re-code their own website to use native advertising rather than a third-party network. I believe this to be an excellent practice, but I just don't see Microsoft going this route. I'd love to be pleasantly surprised though.
It even works without a network connection.
I'd think the user agent string is more likely to cause a huge discrepancy, as many frameworks will be utilizing polyfills and employing different technologies depending on what each browser supports. (Or, in the case of the user agent string, what the framework thinks the browser supports, regardless of how correct its assumptions are.)
If I understand both tests correctly, Opera ran with adblock and battery saver enabled (those are apparently not default settings), versus Edge without adblock, on sites which supposedly are ad-heavy - this will bias the results towards browser with adblock enabled.
The point to me is that the situation is more nuanced than Microsoft apparently chose to present it.