To the OP, they do provide the raw HTML to Polaris Components (this is what I use -- I don't know React). Not sure if that's the same as HTML "components" though.
I had previously built a rails app using Shopify CLI and it failed review due to some endless cookies loop that I could not reproduce caused by their gem. In the end, I just rolled my own OAuth / user database / Billing - but talk about a waste of time.
This is 100% my experience as a developer of Shopify POS plugins (building features that "should" just be included in the core product). I entered their ecosystem 9 months ago bright-eyed with the hope of being the captain of my own ship and hopefully building a living; I now feel like I have essentially signed myself up to build core features for their app (and dealing with frustrated customers who, rightfully, believe this feature should just be free and included), with the added handicap of being a third-party developer, and making significantly less than what I would make if I simply worked or contracted for them.
For now my apps are growing each month, but the culture and practices have left a bad taste in my mouth such that I also know that this is not for me in the long-term, and hope to someday exit their ecosystem.
