It is a welcome feature, but themers should understand its limits and that this new UI offers more power to users, not less.

Builders and themes can limit access to UI using block editor settings - https://github.com/WordPress/gutenberg/pull/39566.

There's also block type level control - https://github.com/WordPress/gutenberg/pull/39568.

I will publish the dev note before WP 6.0 RCs.