This is a conversation that happens every time the draft is near. Every time. It's not about drafting for what you need, it's about drafting the better player. If there's a "big" player available that projects to be great then sure... but removing options just because of what you need or their size is just bad for the team.
The balance doesn't really matter because that player is at least 2-4 years away from making any sort of impact at the NHL level at the minimum. In that time teams change -- players move on, players develop and players grow. What doesn't change is a need in drafting the best possible player at that time. We drafted Cowan despite having many "small skilled" players and many thought it was an overreach bad pick... and now he's untouchable. This is why you have trades and you have signings, to supplement your team in whatever it needs.
Mews is 7th in all of OHL D scoring -- 3rd among draft eligible D and the youngest of the group. I'm not sure I can take that seriously that his offense hasn't "exploded like many hoped" when he's obviously among the top of the scoring leaders among D on a pretty average team.
"Mews isn’t the most spectacular player you’ll ever see, but he’s the kind of very reliable two-way defenseman that coaches will feed minutes to. He’s very intelligent at both ends of the ice. He skates well and can both skate and pass pucks out of trouble."
"I can confidently say that Mews might have the highest upside out of any defencemen in the class. When breaking down every trait I look for in a young athlete, I struggle to find many flaws and things that Mews isn't capable of doing at an elite level. Henry has consistently been the best 2006-born defender in Ontario, along with Sam Dickinson, and I still think these two are far above the rest of the pack. They are very different players who will bring a different style of play to pro hockey, but both are elite in their own respects."
Here's an actual scouting report for Mews that I think it's a lot more fair that showcases a lot of great things he does but also the bad, which is definitely an issue and part of the reason he's ranked where he is: