POBJOY
The largest problem facing GA in the UK has nothing to do with leaving the EU.
All the problems detailed above will impact UK GA as much as they will the Aerospace/Air Transport sectors following UK becoming a "Third Country" after 29 March 2019. Think EASA Part-FCL licensing, engineering licensing, airworthiness, air traffic control licensing etc, etc.
I do, however, agree with the main body of your post.