Default 'edit' gets overridden/changed by VE to be 'edit source', which is misleading here - JSON is the source; this is the rich editor.

Possible options include:

1. Getting VE to stop blindly ploughing over every content model when its function is to add a new editing mode only to a specific one
2. Killing the normal edit tab entirely and just adding a new one VE or other such extensions won't mess with
3. Giving up

2 is an insanely bad idea because it will break skin compatibility out the wazzoo - turns out a lot of skins in fact do expect the main edit tab/button/whatever to be listed in the navigation info under 'edit', and indeed usually expect it to be in that precise spot/order in the array as well, so randomly changing that is going to cause some problems.

1 might work and has been filed under T222115.