Yup, fully agree. Thankfully for most of my client work I don't need WordPress theme-ing at all, so I have a custom plugin that disables that, and instead allow

Yup, fully agree. Thankfully for most of my client work I don't need WordPress theme-ing at all, so I have a custom plugin that disables that, and instead allows me to integrate into WP (so that I get all the WP core PHP functions as well) a PHP framework installation (for example Laravel) where I do all my data-and-front-end wrangling instead. It also supports replacing the front-end with a custom React app, if I wanted that, leaving WP as just the API and admin panel. And as for letting customers edit custom data structures, I still roll with Advanced Custom Fields plugin for that, because it's 100x faster than making the equivalent functionality for the block editor. I do hope they simplify that API at one point though.