I'll put my money where my mouth is. We at Outpost will host your site on Ghost for a year for free and migrate all your substack subscribers, with the only caveats that 1) you put a tip jar link (either to Ghost's or Outpost's) at the end of every email with some text like support us being on an indie platform and 2) at the end of the year or earlier report how it went.
With 66k subscribers you could cover that without even really trying by setting up a $5/month donation tier or putting a tip jar on the site. With a tiny bit of effort, you could make thousands a month.
Substack lets you get away with sending that many emails without attempting to monetize because you pay them in clout and with your reader data.
I think they are getting the better deal given how good your writing is and your reputation.