blog page showing as home/landing page despite template change and reading settings

You should read up on the template hierarchy.

page.php is automatically used for all static page. It should NOT have a “Template Name” header in it.

home.php is for styling your BLOG page. It should have a loop that can handle multiple articles.

front-page.php is for styling static home pages.

index.php is the fallback template for all of the above files.