To each, his/her own, but I'm a bit confused by your analysis. Sure RTM isn't design "for" GTD. It's designed for flexibility which allows it to be used for GTD. It's the most flexible system I've seen and has allowed me to grow, change, and learn. Frankly, it's the closest thing to paper that I've found in a cloud-based system with offline access.
Originally Posted by May
How would Evernote be more convenient? I use Evernote for my reference system but I would find it astoundingly limited, inflexible, and slow as a robust GTD/task management system. If anything is designed "for" GTD, Evernote is much less so than RTM.
There's an inherent convenience limitation in Nirvana also: it's web-based and doesn't have an app for offline use. I would hate for my ability to review or reference my tasks to be tied to my connection. Very inconvenient.
Everyone has their own requirements and needs for their own productivity management. To each, their own.