You're not talking about depth here though. Depth is about relative quality down the lineup. That we have. Whether it's the kind of quality you'd like is a different topic.
Kadri got suspended because he can't control his emotions. It's solely on him. There are ways you respond for the team, and ways you don't. Kadri responded in a way that hurts the team because he couldn't handle his frustrations, even though he was asked to reign it in on the bench. That situation really has nothing to do with anything else than him.
I agree Kadri did it to himself. However, here is a clip of all the big hits between Leafs and Bruins in this game.
If you can, watch the entire clip and ask how Bruins didn't get called for multiple dirty hits. I see non calls for dangerous high hits/stick work/cross checks. The hit Pastranak threw on Muzzin was a penalty but could have been a suspendable play as he launched himself into his head.
Really dangerous.
Two non-calls in particular set Kadri off.
Watch the knee on knee Kadri takes at 1:52 and the Marleau hit from the side, into the turn buckle at 3:36. What Kadri should have done is drop the gloves, he shouldn't have used his stick obviously. This doesn't excuse this type of reffing which encourages such dirty hits. No calls put everyones safety at risk and turn the game into a wrestling match.
I was one who agreed Kadri had to be traded, I'm not excusing his actions, I am explaining how it gets to that point though. We're all human and if you feel one team is getting away with dirty stuff against myself and my teammates, there is going to be a reaction. If refs make some calls early, the teams calm down and everyone is on notice. We have to decide, do we want good, clean hockey or thugs and fighters? If it's the former we aspire to, you absolutely need consistent, by-the-book reffing.
In terms of depth. I don't want to play coach, but here is how I see it. We need some players down in the lineup who can pin the other team in, win puck battles/dig out pucks, often a line change occurs in such situations giving a favourable match up when the opposition it trying to retrieve the puck. Hemming other teams in, "grinding it out", making it tough for them to get momentum. It has a macro effect on the game, or a series. In todays NHL no team does this better than the Bruins.
These players aren't the key to winning, but they are the unsung heroes on the 3rd or 4th line.