A couple of people have already touched on a couple of big issues. Right now you only have one premier offensive threat. Beyond Tarasenko none of your forwards scare anyone or need to be matched up against. That does mean that your forwards are trash (they are not) but it is a lot of middle six talent and Tarasenko is your only top line threat. If the Hawks and Blues play the Hawks have 3 of the 4 best offensive forwards (Kane, Panarin, Hossa, Tarasenko). The rest of the rosters match up fairly evenly.
The penalties and aggressiveness can also work to your detriment. Focus more on skating than hitting. And get rid of Reaves or teach him to play a different way. Every once in a while he has a good game where his forecheck causes pressure and turnovers but it is his only skill and when it isn't working for him he is nothing but a liability. The Hawks have brought in "tough" guys like him in the past (Tootoo, Carcillo, etc.) but they do not allow those guys to goon it up or play dirty which might cost them a game. They make them play hockey and be solid defensively (there toughness is just there just in case the other team does something stupid).