There's no real chance that Ottawa would have offered what San Jose gave Karlsson, especially in terms of contract structure (i.e. high up-front bonus structure for the first 4 years).
https://www.capfriendly.com/players/erik-karlsson
Factor in how well Tierney and DeMelo have worked out, the fact that Norris signed and they got the conditional 2nd rounder, and how risky it would have been to chance trading Karlsson mid-season (especially in a season where he missed 1/3 of the games), and I think you have to concede that Dorion didn't do too badly in this deal.
It's also good to see that they signed Duclair to a reasonable 1yr deal. This next year will be the real test for him, to see if he's got a long-term future with the rebuilding team... or if he could be flipped at the deadline, as could be the case with the likes of Tierney, DeMelo, Boedker, and Pageau.