The two words overlap but they are properly used in different contexts.
If a person has ordered 20 boxes of tiles to tile a floor and finds that they are not sufficient to cover the whole floor, that person is short of one or more boxes. That's to say that more are needed.
If a supplier has an order from a buyer for 20 boxes of goods and only delivers 19 ...
It isn't really a sentence, but it could represent casual spoken English (or interior monologue). As "bad grammar" there is some flexibility, but "Not surprisingly" is the best "bad grammar".
For good grammar of formal English, you would need to incorporate this into a sentence, and then you would probably want the adverb.
In the U.S at least, I doubt "usual" alone would be common. If the responder's intent to the question of "how was your day" is to indicate that nothing noteworthy happened, the responder might say
It was [routine/ordinary].
It was a [routine/ordinary/normal/usual] day.
I cannot firmly articulate a reason why "normal" or "usual" as an isolated ...
Its allowed (its clear, understandable) but there are better ways of phrasing it.
In the context of a thank-you letter (that is addressed to your friends):
Thanks to you, my friends and the best role models I could hope for.
This kind of exaggerated style is common is such contexts. In this is normal to use more words than needed. You could, for example ...