But you are running WebKit in all four on iOS :) Because right now Apple doesn't allow other engines. So whatever it is that consumes batter, it's not blink or gecko.

My points of comparison are the macOS versions, where the difference is staggering. Architecturally macOS and iOS are very similar and it’s traditionally been quite rare for either engine’s team to focus squarely on improving efficiency (it’s always speed or features instead, with efficiency as a trailing afterthought), so there’s no reason to think that Blink and Gecko for iOS will be any more efficient than their macOS counterparts.