For years the it was advised to add visual settings to the customizer. And it was the right thing in my opinion.

Now that there is something new in development. That is not even fully worked out and stable for a few month/versions so that developers could have time to adjust there (free/open) products to it. Suddenly the core is so arrogant to break all other developers stuff with full intention.

WordPress celebrates itself for being backward compatible. This does not mean just the source code.
From the Philosophies "Design for the Majority" also means to have a majority of developers in mind that have build on top of WP. Not all developers have the time to adjust there plugins and themes everyday to the latest Gutenberg changes.

Because the core team is to lazy or ignorant to build a off ramp from customizer to FSE the solution is to offload the work to hundreds of support staff? Creating thousands of (unpaid) hours of work/communication. Something that could be prevented by putting in a few hours of development work.

In stead the settings inside the customizer that have moved to FSE could show a notice and a link to the new place. Something well build software does like WooCommrece with there change of coupon menu location.

Have we not learned anything from 5.0?
Do we need another "Classic *" Plugin to fix the narrow view of the core development team?