I'm sorry, but I just flat out disagree. The Bruins have had some of the best depth in the league and it's helped them get to the playoffs each year that Claude has been here. You raise Marchand as a counter-argument, yet he was able to be broken into the lineup quite fine. If a young guy is pushing themselves into the lineup, the Bruins have found a way to get them ice time. If there is one thing that I'm not worried about when it comes to Claude and Chia, it's breaking in young players - they've done a fantastic job over the years.
I tend to agree with this when it comes to my view of Kelly. Sure, in the regular season, Kelly doesn't have tremendous value, but in the playoffs guys like him can almost double their worth with the way they play. The depth they can run out there is what got them to the Cup last year, and bringing him back makes sense.
Both signings suggest they continue to value Center depth over all else, and also that they see Seguin as a wing. With Kelly and Campbell back, and Krejci looking like he's going to stay, I suspect they are going to slot Seguin back with Bergeron, and then the only thing they have to do is fill out the 3rd line wing spot. Caron would have the best chance, but I imagine Knight, Suave, and Spooner are all considerations for 3rd line duty.
Given the options out there, and the fact they could put any free agent winger on the top two lines, that leaves anyone from Huselius, Doan, Penner, Langkow, Hudler, Whitney, etc as options. Parise is still a dream, but I think that grows more unlikely by the minute.