Even more concerning than browser-specific websites is seeing browsers ship non-standardized features just because they want them, not behind any vendor prefix or flag. There was a time when web developers would have got out the pitchforks if a browser was doing this, but I sense some complacency seeping in.
These days, the vibe is more centered around complaining about other browsers lack of support for things. For example, one browser ships something, we see one green dot in caniuse, and we lambast the other browsers to catch up. Instead, we might ask, was it a good idea to ship that feature yet?