in fact, Jumpluff can come in on anything it resists- Fighting, Ground, Water, Grass (all of which are really commom) and lock the opponent in that move. This forces the opponent to play extremely cautiously, because one thoughtless EQ could end the match.
The reason Whimsicott does not do this well is because Whimsicott can not put things to sleep. Obviously, if you miss sleep powder, that sucks, but Jumpluff has a lot more bulk than it seems.