The comparison here is, "serving your content, and then doing whatever the heck you want", and "dynamically fetching all of your core content on the fly after synchronously downloading and executing all of the auxiliary content that >85% of your users do not care about."
I think Youtube is overengineered as well, but at least Youtube has the good sense to prioritize loading the video first, and the recommendations/comments second.
It is surreal to jump from a thread with a Google dev telling me that user-agent scraping is necessary because progressive feature detection would require shipping unnecessary polyfills to modern browsers, to a conversation with an Imgur dev telling me that because 5% of their users need a special feature, everyone should wait twice as long to get core content served to them.
I realize these aren't the same people, and the web development community is diverse, but... I don't know how to reconcile those perspectives. We will jump through so many crazy, horrifying engineering hoops to get bundle sizes down: using statistics/user-behavior to calculate dynamic bundles on the fly, user-agent sniffing, compiling Javascript frameworks, prefetching URLs, HTTP2. But serving an img tag with our core HTML is a bridge too far?