That's because it is. If you're smart/lucky you can get a White Pikmin to do significant damage to an opponent, but the rest are kind of bad. People keep telling me "it's free damage" but it's not really free when
- It gets my Pikmin killed, thus making me lose some of my damage output and recovery
- You can easily hit them off before the first hitbox comes out
- You can't perform a combo and sneak a Pikmin in because that takes too much time and the opponent will be able to act if you do which makes you lose overall damage.
Literally the only way it does extra damage is if you stop a combo and throw a Pikmin on the opponent then successfully reset the combo before they can knock the Pikmin off, which is damn near impossible. And to make matters worse, the more damage the opponent has the less the Pikmin will hit them. I think once they're over around 80% the Pikmin will only hit them twice before falling off, or in White's case, before it explodes.
Also exploding White Pikmin sucks because that's our real damage output right now, and if the Pikmin manages to explode it's usually because we managed to combo the opponent while White was hitting them. So to stop it from exploding we have to purposely drop our combo to whistle the Pikmin back. And to make that scenario even more ridiculous, we have to memorize exactly how soon it's going to explode thanks to its "fuse" being shorter if we throw it at a high damage opponent and Olimar doesn't really start to secure kills before 100% or so, unless the opponent is easily gimped.