It's common for archive templates like Index, Archive, Category, Tag to display post content the same way. At the moment, if you decide to change the design in one template, you then have to replicate that change across all the other templates as well. Traditionally themes would include a content.php template part to circumvent this.

If you try to do this in the block editor, the experience is a little funky (#44160).

An alternative solution would be to make the Post Template block a bundled template part in its own right, with a new semantic area (similar to header / footer). A benefit with this approach is that it immediately becomes possible for users to edit in focus mode, swap with other post-content template parts, browse patterns, etc.

cc @WordPress/theme-team for thoughts.