Aight here we go.
The Ottawa trade, while likely suitable in value, isn't great for Ottawa positionally. Sadly, White is arguably Ottawa's best center right now as Stepan wants to move back to the US, Norris is a rookie experiencing big even strength struggles, and Chris Tierney is an enigma that somehow produces while having awful metrics. Until Stützle is moved there, or Logan Brown is given an extended look to take the spot, or one of Pinto or Norris develops into the role (unlikely), White will hold a ton of value for the Sens as their de facto 1C. Otherwise he's an okay middle 6 player signed longterm who has some upside and reliable defensive IQ that's translated well in the past when the team was stronger.
On D though, the Sens have Chabot, Brännström, Wolanin and Reilly down the left side. It's not great and Pettersson is almost certainly an upgrade at the position, but he will forever be behind Chabot and could already be behind Brännström depending how Pettersson would look in DJ's system (especially since Erik started the season very strong). In the prospect pool, the Sens have Sanderson who also plays on the left side and so they've already caused a logjam with their 3 biggest D of the future being on the same side. It's poor asset management to go out and trade for another LHD that at best plays on their 2nd pair as a #4 for this year alone, and very quickly gets replaced and pushed to a 3rd pairing D when Sanderson comes in. Especially when, again, as mentioned, they'd be trading a guy who is currently their 1C. Down the line White likely projects as a 3C, but he's too important right now.
As an aside, it's also really humourous how frequently Pens fans make White for Pettersson trades and then when Sens fans (
@csick @PLDGEY @sensibleguy ) say that Ottawa might not be interested because of positional strength, you guys get all defensive and go "well White is garbage anyways, have fun staying bad, SENS SUCK PENS RULE, KAPPA DELTA PSY FOREVER BABY LET IT RIDE YEAAAA". If he's so bad, why is it always you guys trying to trade for him? If Pettersson is so good, maybe you should keep him for your depleted D core or to cover for Matheson and Ceci. Seems the Pens are in 23rd right now without a 1st round pick, which was a song the Sens were singing not so long ago. The responses give off the same vibes as those guys who get rejected by girls and then go "well you're fat and ugly anyways".