Focusing your disappointment solely on Brady is lazy, and frankly a poor analysis of the team as a whole. Everyone knows he has some warts defensively. He is clearly trying to work on them this season. Team results haven't been there. Tkachuk has been the second best forward on the team. No issue with his effort either.
This is still a bottom 3rd of the league team. Has been similar for 3 seasons player wise. They just aren't that good of a team. They don't have winning habits to fall back on, because they have never won consistently. They don't have a high skill level, not particularly physical, pretty slow overall. No real identity other than that of a team that doesn't know what it is yet.
Has been some glimpses of things finally coming together this season, but it hasn't happened. Swap Brady for another winger who produces a bit more, or is a bit better defensively, and the team is still bad.
Need more from all the players, Brady included. Probably need better players throughout the lineup realistically. The likelihood of patching up a team put together by Dorion and turning it into a perennial playoff team is a massive challenge.
The captaincy is overrated by hockey fans. He's one of the players on the team, who has a leadership role. Their are other leaders as well. He wears the C, and takes the blame from some, but he's just one player on the team in the end.