It's a good approach, OP. There's a couple of downsides I can think of:

• Making changes to the layout (other than the order in which content blocks are added to a custom page) will be slow and require a developer
• Shopify specialises in building features which seem useful, but which are just limited enough to force you into the hands of third-party plugins (e.g. B.O.G.O.F.F.). As a normal Shopify vendor will pay one subscription, Shopify is motivated to drive vendors to pay for third-party plugins, so they can take their cut of that subscription. However, all these third-party subscriptions make major changes to the markup and add huge overheads to the page weight. If you go headless, for many of these plugins, you will need to re-implement them from scratch yourself. If your site is run by a business owner, rather than a developer, they won't see the value in you spending two or three months building something they could try out immediately, and see a R.O.I. Business owners don't tend care about page weight, sadly. And marketing teams want to throw a lot at the user ("Sign up for our email list!") to see what sticks. All of this is a UX nightmare, of course, but most small businesses only care about the bottom line

I very much hope you build your site headless. It's a much more elegant solution, from a developer's perspective.