The opposite is the case. Overall, being too lenient in what code accepts and applying heuristics will lead to way worse problems down the line. For example, you want your compiler to fail hard instead of saying: "Oh, this isn't a pointer, but I'm sure you meant well, I'm just going to treat it as a pointer!"

In this particular case, it seems to me that the hints serve no purpose and should be abolished, and in the meantime fully ignored, altogether. All necessary metadata is contained in the image file, and browsers should also be (relatively) strict in what image files with what metadata they accept, for security reasons alone.

And if they also went so far as limiting file size, the perpetrators that clog up bandwidth by putting up multi-MB favicons would catch on much earlier (or at all), too.

So what actually is the point of those hints, if browsers have to fallback anyway?