Minimal difference but could be bigger if someone gets injured. The point is we lost depth at a really important position to bring in a unique but unnecessary skillset at a position of strength.
Here's the thing though, do you think there's a significant difference between Blueger and Sundqvist at this point? I honestly don't think so, I'd honestly argue that Blueger is better than Sundqvist or at least very close to Sundqvist currently. The Penguins lost someone who'd probably be their 5th center on the depth chart, and that's with assuming McClement doesn't sign, Rowney is the 3C (aka they don't trade for another center) and Sundqvist would be above McKegg. Saying Reaves was unnecessary is fair, acting like Sundqvist is anything more than a marginal loss isn't fair.
I mean, let's look at the Penguins current center depth beyond Crosby and Malkin:
Rowney: 7 points in 27 NHL games, 21 points in 26 AHL games last year
McKegg: 7 points in 46 NHL games, 4 points in 7 AHL games last year
Blueger: 31 points in 54 AHL games (with no PP time and having extremely tough defensive minutes)
Johnson: 37 points in 42 NCHC games (was called the ZAR of next offseason, put up those numbers as a sophomore)
Dea: 34 points in 73 AHL games
Sundqvist: 0 points in 10 NHL games, 46 points in 63 AHL games (while getting PP minutes)
Is Sundqvist really above anyone in that group? I'd honestly say no. I'd definitely rank him below Rowney, I'd probably rank him below Blueger based on how each player was used and I think Johnson will pass up Sundqvist this season as well (if the hype is true that he would have been the ZAR of the 2018 offseason, the Penguins got a gem with him).