Even in order to be "only" compliant with modern specs, there is no escape from creating an extremely complex piece of software. This hurts real world security for everybody to the point where it might be better not to browse at all on machines with which you can access private servers or your private mail or conversations. It would be nice if there were some smaller browsers that didn't focus so much on backwards compatibility, but on leveraging the most important features so that most of the web could be browsed, still without sacrificing end-user security by implementing each and every feature and performance tweak. In the end, the OS and the browser should be trustworthy by the user.
[1] "Overall code quality: After reading Moxie's RedPhone code the first time, I literally discovered a line of drool running down my face. It's really nice." http://blog.cryptographyengineering.com/2013/03/here-come-en...
[2] http://www.ecma-international.org/publications/files/ECMA-ST...