This is a great talk!
The business models that support much of the content on the web don’t favor better performance. Nor does the culture of many organizations who end up prioritizing the next feature over improving things like performance or accessibility or security.
Users need to be able to find the website. They need to be able to use and perceive it correctly, they need the website to function correctly, they need high-quality content, and they also need to have a good experience after their visit.
This article is about style performance improvement with Shadow DOM, but it also contains a useful comparison of selector performance between ids, classes and data attributes: