You need elite players in their prime, with a good supporting cast.
It doesn't matter if your great players are big, small, forwards, D or a goalie.
A lot of teams win with a great goalie and defense. Last time Pens won their only top end D (Letang) hurt the whole playoffs.
Though obviously the game is getting faster. So it will be harder and harder to win just by playing a all out defensive game. Also, your D needs to be more mobile than ever.