Have you had much luck with slots? I have a project using View Components that leverages slots. I've tried migrating to Phlex, but the lack of explicit slot support has been a bit frustrating.
To create them declaratively (not needing to call them in a set order) you just create a module that defines `before_template` and calls `vanish`: https://www.phlex.fun/miscellaneous/v2-upgrade.html#removed-...