I like what the OP has written and I empathize with what it says. Daydreaming does seem to cause some issue with my SA.I respect all viewpoints and I'm no expert but...sorry...nope.
Quite a lot of the idea that daydreaming causing social anxiety is based on false principles. The idea that there are certain types of people who are "introverts". This is the type of thinking behind personality tests, the idea that something that is constantly in flux can be accurately measured and assessed by answering a series of vague questions. Personality tests do often work the same way as cold reading works. The person doing the test says: "you tend to be more introverted" and, if that statement chimes with your understanding of yourself, you agree with the statement and then say: "wow, that test really knows me". I'm not saying that talking things over with a qualified mental health professional and doing tests in that environment is a waste of time. That's essential if you're in any doubt about your mental health. But pop psychology these days thrives on the notion that you can go online, answer a few vague questions about whether you occasionally don't like going out on Tuesday and, all of a sudden, you're an introvert.
We're a mixed, complicated bag of so many things constantly in a state of flux. We change and circumstance changes us. Entertaining Freud and his successors is a fun job but you could drive a truck through the plot holes in most of the thinking.
Daydreaming means you lose contact with the real world? Erm...what exactly is the "real world". For a start, a lot of the things that exist in the real world started off inside the heads of people. In other words, if people hadn't day dreamed, stuff that is now in the real world would not be in the real world. Focusing on the internal is not about escapism. Withdrawing into a fantasy world is very different from daydreaming and reflecting on the inner reality of the individual. Indeed, SA distorts the inner reality of the person so it is a good thing for people with SA to focus on their internal reality. The solution is, so often, inside the person with SA. Yes, one seeks therapy in the outside world and social interactions in the outside world. But, if in your internal reality you don't think you're worth fighting for, you're not going to seek therapy and or move on to social inter actions in the "real world".
However on the whole I think I agree with you. Under the myer-briggs test I think it described me pretty bloody well, but ultimately I see people are too individualistic to be put under such a blanket.
It's definitely one of the issues, though.