Shoelace is more akin to Bootstrap. You can use it for quickly tinkering, prototyping, or as a foundation for your own design system.
One thing Shoelace doesn't provide right now is a set of base styles. I've considered offering these as an opt-in CSS class or a <sl-prose> component, but I'm not sure it belongs tightly coupled with the library.
On one hand, it makes sense to provide a single "theme" that styles both components AND the underlying website/app. On the other hand, this will make themes very opinionated and potentially overbearing. I still need to think about this more.
In the meantime, you can use something like Tailwind's typography plugin [1] to handle base styles and use Shoelace in lieu of Bootstrap. IMO Shoelace + Tailwind is a great combination for those who prefer utility classes.