Ignoring the GS/Blancpain vs Rolex argument, the idea of trading up is consistent with collecting.
My earliest collections were marbles, corgi cars and comic books. I didn't do baseball cards but they were similar. We were always looking for a marble we didn't have or a missing comic number, trading two or three for the one you wanted.
The concept isn't that strange to me. Perhaps some folks took you too literally, or your question about going from a GS to Rolex was too broad. There are many, many different paths for getting from GS to Rolex, but probably few that involve one trade.
You also phrased your question as trading from GS/Blancpain to Rolex as going from a lesser brand to a better brand. That is arguable, which is how many people responded. I would agree with people who say you're not necessarily going up. So your question has several layers in it, with the concept of trading, as well as comparisons to brands, not to mention insulting the audience to whom you addressed the question. You got the responses to the question you asked. If your responses didn't meet your goal, rather than attack the respondents, you would have had better results by rephrasing your question and perhaps shaping the narrative by continual interaction. Instead, you read like a petulant child.
Going back to your question about trading, it can part of the fun, can give a collector a goal and direction, but takes time and can be incremental.
Your goal of getting a sub for your dad is commendable. Given the current watch economy, you might be better off buying a sub directly because they have dropped and some nice vintage pieces are available. But trading and selling less expensive watches to try to turn them into one more expensive watch is not straight forward or easily done. It's easier if you don't burden yourself with thinking you have to come out ahead financially on every watch you sell or trade. That's unlikely, and then you're acting like a dealer that you disparage. Consolidating several watches into one more expensive watch that you give to your dad is a fantastic way to focus your collecting watches and probably one of the most rewarding experiences you could have. As for how to go from GS/Blancpain to a Rolex Sub, that's impossible for me to say, as there are too many possibilities.
Best of luck.