Pichu is indeed one of the worst fighters in smash, especially since it takes a little damage every time it uses an electric-based attack, but it also has some good points.
An example would be that when it's Skull Bash (side special) is fully charged, it can do more damage than Pikachu's Skull Bash. It is the lightest fighter and has above average dashing speeds, and to make up for the recoil, many of it's attacks have higher attack or knock-back.
No I do not main pichu I just so happen to randomly know this