Why not have both?

You send your newsletter, but show the contents in a blog post format as well.

Yeah this the standard approach, I don’t know of many newsletters that don’t make their writing available elsewhere.

I do. In my experience a lot of newsletters that are monetized in some way or another don't get published on the web.

Exactly this. As a reader, I want to search old posts when I have time to read them and am looking for a specific topic, rather than wait for a weekly email and hope it's relevant.