So who are the top offensive forwards who were bad defensively who became above average NHL defenders?
The better question would be how many high scoring forwards are truly held back or are a net negative because they are bad defensively?
The pool of young forwards who are classified as poor defenders is significantly smaller than the pool of young defensemen that get hit with the label. For some reason people will turn a blind eye to a high scoring forward who is a liability defensively but if a highly skilled defenseman makes a few mistakes defensively, it's the end of the world. Some of it has to do with the old school people that look at a defenseman as a
defenseman. People are also more apt to recognize a defensive mistake by a defenseman more so than one made by a forward. A mistake by a forward defensively can hurt just as much as one by a defenseman.
Defensemen are a bit different, since few offensive defensemen are good enough to compensate for bad defense, most are under more pressure to improve their defense when they hit the NHL (and the ones that don't tend to wear out their welcome, like Carle).
That's your assumption, but it's not really true. What if I flipped that around and said "few defensive defensemen are good enough to compensate for bad offense." Is that more believable? You can be the worst defenseman in the world, an absolute train wreck in your own zone, but if you transition the puck up the ice effectively and convert on your opportunities in the offensive zone at a high rate, you are going to be an asset to your team. Carle wore out his welcome because he stopped scoring. Teams are still paying for points.
The two most valuable defensemen this season were Erik Karlsson and Brent Burns (Hockey Reference had Burns as the
most valuable player overall and Karlsson the 2nd most valuable
skater behind Burns) . Neither known for their defense, get dumped on all the times for their mistakes, but they generate so much offense it doesn't really matter what they are doing in their own zone. You can throw in Josi, Byfuglien, Krug, and Werenski in there too. Some of those guys aren't even bad defenders, but they get labeled because they are small and/or really offensive.
All I want to know about a player is does he drive play and does he convert his zone time into chances and goals? If the answer is yes to both questions I want him on my team.