In reply to Sayontan Sinha.

The customizer is a good example of bad apples ruining the experience for others. The team allowed use of the Settings API and other custom implementations for two years after the customizer. However, there were so many security issues, broken interfaces, and just generally bad coding practices that theme authors were not proving the value of alternative systems. There were those of us on the team who fought to give theme authors a chance (myself included at the time), but in the end, we caved because few lived up to expectations.

I think you'd be hard-pressed to find anyone on the review team who thought the customizer or its requirement was a bad decision. The bad thing was pretty much the total abandoment of continual improvements of its API and documentation from core WP.

While I am no longer a member of the team, I have wanted them to go this route since Matt first proposed it a few years back. Open the gates, let theme authors who don't move along with standards fail or develop for their own circle of users. Let them get blamed for when they inevitably break plugins. Let users downvote them for not internationalizing their themes, creating a11y-ready output, and disregarding user-defined settings. But, also let them flourish and try out new ideas.