This is a unique feature of Kratos/Hydra, you can use your own frontend components. With many other implementations this is not possible.
What do you mean by "much more opinionated client", there is a set of standard flows that your app has to handle and thats it for most cases.
If you want out of the box components they also have a paid version for that (and code examples in OSS)
If you want out of the box components they also have a paid version for that (and code examples in OSS)