I think TIFF has a number of advantages there. It was from the beginning an interchange format, so it had the opportunity to look at a bunch of existing formats and extract the commonality. It's also not an application format, so the pace of change is slower and more controlled; it can trail rather than lead. And it is of course a standard, which means a different set of dynamics around how things get added and how clear the specs have to be.

That's not to say it isn't great; I could well believe it. But I'm just not shocked that PSD and PostScript have ended up being a bit of a mess over the decades. I doubt I could have done any better.