However, I do believe you can build a lasting saas business with a strong backend / weak frontend, but can’t do it with a weak backend / strong frontend.
I'm actually impressed and surprised by how many frontend jobs DevQuarterly sees (https://devquarterly.com/insights/trends/). Big tech companies typically have many more backend developers than frontend developers. It depends on how many of those fullstack jobs are frontend heavy, but from what I've seen these job postings from smaller companies are often looking for frontend developers with some basic backend and cloud skills to build a product 0 to 1. Backend at that scale can be quite simple and is not out of the wheelhouse of a frontend developer that can actually code.
Doesn't look like many people have bought into Hotwire with Rails ;) The "component and compilation circus" is pretty easy these days and improves the potential for your site. People see the billion dollar SaaS companies with fancy websites built on React and follow them.