‘And, anything you can do starting from scratch, you can do quicker and easier within the GOP.’
Not necessarily. Sometimes the structure is degraded to the point where it would be simpler, easier, and more productive to demolish it and build a new one. New pipes, new wires, and no GOP-e termites.
The structure is, basically, if you win elections - either for legislative office or for party office - on the local, regional, state or national level, you control the party; and, to a certain extent the structure.
If you can't win elections on these levels in the GOP with your people or manage them effectively when you do, you can't do with a new party either. It's the same tasks, skills, people. Anybody can build a party comprised of their kitchen table. Growing to a size that controls legislation requires greater skill.
What's harder is doing it from scratch when there's already a structure in place, ballot access, assets, systems, etc. etc.
I sometimes wonder if those that complain about the GOPe have ever participated in electing their local, regional and state party enough to understand that this is what the party really is - not some nefarious 'them'. Are you aware of this?