And to be clear, I don't think Johansson is any sure bet to be an NHLer, never mind a good top-4 guy. So I won't be let down if he doesn't make it (I think he does have the potential and I'm rooting for him). Size will certainly be a factor for him, simply because he is indeed on the smaller size. But he's being talked about here like it's some major issue. Like, an outlier. It's not. It's simply one of the many things young, developing players have to work on, and in this case it's a relatively small issue, given the kid's other strengths.
The first statement is categorically false. Dmen under 180 may be an exception, sure, but they aren't all that rare. By my count, there were about 14 dmen this year who came in under 180 and played either in the top-4 or a majority of the season in the NHL.
NHL Stats
The second statement.... has anyone said it isn't a factor? Looks like it's mostly a debate of
how much of a factor it is.
In general, it's of course a factor. In specific cases, there's much context to consider to decide
how much of a factor it is. Skating, skill, work ethic, etc, etc..... all things that can mitigate size.