Actually, a skilled Yoshi player can adapt and over come swords. I've beat a fair few, lost to them as well. They are a good defense against a Yoshi, but if they learn your setup, they can over whelm you as well.
Learn to predict Yoshi's paths. Learn to out space his attacks, and counter as soon as you can. Parries are also a good way to beat them. I've lost to a few counter attacks, like against Palutena. Ness can be a challenge to a Yoshi, provided the player has more then spam PK Fire. Although the PK Fire trap to get batted off stage is effective if you can't break free of the fire fast enough.
Not sure how Pikachu is these days, but he used to always own me, but that was back in Smash 64. The eggs can be reflected, and never fall for the Yoshi standing near the ledge when your above 75% damage, thats a dead giveaway he is going to try and drop you off the stage. Otherwise, just do your best to out do the player playing Yoshi. Honestly, I get beat by a good amount of characters with skilled players behind them.
I hate to say it this way, but Yoshi can be a crap shoot, but even a skilled player with a heavy can beat Yoshi. I've lost to King K. Rool before, it is really hard to get in a good hit when they are on the defense. That crown is annoying as well due to it's boomerang effect. Most of K Rool's attacks can over ride Yoshi's attacks as well if timed right. Hope this helped.
Also, I write this under my own opinion, I do not speak for all Yoshi mains, just out of my own personal experience.