It's comical that some of y'all think Dark Horse's 1.5 billion views - which is an extremely impressive feat, no doubt - versus Bad Romance's 725 million views equates to Dark Horse being the bigger song. Not only has YouTube and streaming in general grown exponentially between the release of both songs, but y'all do realize that Bad Romance was for a time the most viewed video - not just music video, but video in general - on YouTube, right? That's indescribably more difficult to achieve than being part of a "1 Billion Views" club, which, again, is still a very impressive feat, it's just not comparable at all.
The Kats bringing up YouTube views. Bad Romance was the #1 most viewed video on YouTube for over 6 months, if not longer, that would be the mid-2010s equivalent of 2-3 billion views