Historically, I agree with most of your opinions, but I think you are way off base here. Brannstrom has elite skating, but also top shelf IQ on top of that (something Gardiner not only doesn't have, but he is known for making some pretty brain dead decisions.)
I agree that Brannstrom doesn't have game breaking offense like Klingberg for example, but I think he does turn into a consistent mid 40 to 50 point guy. Gardiner has broke 40 points twice in his career and he is 29. Brannstrom will have just turned 20 at the start of this season, and is probably going to play most of, if not all the season with the big team.
He is much better defensively than you are giving him credit for. Yes, a lot of that is skating, but he has an active stick, and his positioning is rock solid. Krug is the absolute perfect comparison. Guys known for their offense, but are very underrated with their defensive game. Erik has some bite to his game just like Torey does, and unlike Gardiner, you will never have to question Brannstrom's compete.
I think “elite skating” and “top shelf IQ” are not on display at this time. I have seen the best defensemen in the league for more than 60 years and he has a way to go before meeting those standards.
Plus his diminutive size is a concern in the NHL playing against the bigger stronger faster forwards. I am hoping he progresses to become an NHL defenseman, but he does not appear to be the next Orr, Lidstrom, Potvin, Coffey, Sjalming, Robinson, Housley, Karlsson, etc.