Simple: Donnypuck plays well against some teams, not so well against others. They are good at playing a pressure game against older/slower teams but if a team plays that kind of game against the Sabres, the Sabres wilt under the pressure themselves.
A good coaching staff would find ways to match the team as constructed up against teams that play the uptempo game more aggressively than the Sabres.
In general it seems that the Sabres historically play only the loose pucks that are at least 50-50 or better.... or even 60-40 in their favor, and don't want to expend the energy to contest pucks they don't think they can control. So when they play a team that aggressively fights for loose pucks, they sit back and let them have the puck, preferring to regroup and organize the defense.
I think they need to be more aggressive on the puck in general. Benson is good at this with Quinn as a good complement. Peterka/Tuch seem to work well as a 1-2 forechecking duo. When they try. The problem is they don't try to disrupt the other teams consistently enough.
You see it used against the Sabres all the time, and a guy like Dahlin who thinks he can take on a double team is especially susceptible if it's done right.... the first forechecker chases the defenseman behind the net, and right into the second forechecker who's coming down on the other side of the net. If the first guy can rush or disrupt the puck carrier, it can cause a turnover. This is precisely what happened on the Stamkos goal last night. They used Dahlin's tendency to make the cute play against him and hung him out to dry.
I've seen the Sabres do the same, but not often enough.