Hello, fellow Pika player! I'm still trying figure out who my definitive main is for Ultimate. I keep alternating between Pikachu and Zelda as a main because they compliment each other well (at least for me).
Pika's fast movement speed and fluent combo ability usually fall into the type of character I like using. Although I've been using Pika as a pummel fighter rather than hit-and-run. We know Pikachu is a character who cannot afford to keep taking hits with his weight.
Anyway, I think Zelda is a decent compliment to Pikachu. She got some buffs from Sm4sh and received a decent improvement, but still overall can struggle in neutral and can be at a disadvantage against rush-down characters.
That's not to say she doesn't have stuff to work with. She has a good defensive game in that she can wall out and pressure opponents with Phantom, her restructured down-B. Side-B, Din's Fire, is a decent projectile. Neutral-B, Nayru's Love, can reflect projectiles and is a good "get off me" move in close range. Her Up-B, Farore's Wind, is an excellent recovery and can also be a surprise move when your opponent is charging a move. It can also be a ladder kill.
Her tools can be used as a bait-and-punish. With effective dashing, you can bait people with her dash attack and grabs. While Zelda still has poor foot speed, her dashing is surprisingly decent. Her grabs have amazing combo ability, such as her up and down throws. Her up-throw and back-throw can kill over 120 as well.
Her aerials also received a buff in frame data. Nair is awesome in a combo, and her lightning kicks (fair and bair) are an excellent finisher. Her dair is also a spike if you hit the sweetspot. U-air is amazing for opponents that are straight above you. It has a pretty sizable hitbox. Her up-tilt is also a good starter combo into a nair or fair (depending on the situation).
Smash attacks are decent too. D-Smash is good OOS, U-Smash always hits if an opponent is directly above you (except when separated by a platform), and F-Smash has a good hitbox and is an awesome punish if you time it right.
I wouldn't say Zelda is a perfect compliment to Pikachu, but she plays a style that differs from him, which has challenged me in my time with the game. I have found it comfortable for myself though. I know it won't work for everyone, but I feel it works well for the time I've had with the game.
Let me know if you have any questions!