Let me rephrase; did they say that we only know of bosses as a list with stages, or did they find something separate that has all the bosses, regardless of stages?
And yeah, oof indeed.
Nah, it's rushed. It's still out the door faster than it needs time. Of course they still did way more than normal, but there's more than enough stuff that was already looking bad just during the last few months. Even the models were unfinished/poor quality even at e3. They slowly updated them.
This is why some modes are only in the data, but not active. No time to do so. It makes sense for Day 1(or very soon) patches to restore those. And probably updates to Classic Modes and/or World of Light to add more bosses. As well as possible Spirits and Music too. We might even get a few quick stages that took longer to finish for all we know. Either way, update patches for modes is practically a given, since not only did the last game did it, there's implications that the modes are in just unchooseable from the datamine information(Home Run Contest included).