Yes, let's extinguish flames with gasoline shall we?
Anyways, why does pikachu lose to Ike? I hear it a lot, but don't understand why.
Pre-patch, Ike had these issues with Pikachu:
-Ike's spacing gets interrupted/punished by quick attack
-Pikachu occasionally ducks under jab and grab
-Ike may have issues landing at low-mid %
-Ike could get combo'd and trapped easily
Even with these weaknesses, Ike still had only a minor disadvantage at most and had a decent chance for it to be even.
-dtilt could easily punish attacks and lead to a fair for ~21%
-grab reward is still good, leading to a fair or nair for ~21%
-Jab is still annoying for pikachu to deal with
-Mixing up sideB and aether makes it annoying for Pikachu to edgeguard
-He's so heavy that he won't be dying until really late while Pikachu can die much earlier.
Prepatch Ike really just had trouble getting punished whenever he whiffed attacks and tried to space against Pikachu. Overall, the damage was decent enough once the Ike finally landed hits/grabs, though.
Now, reduced landing lag on aerials with fixed hitboxes now allow Ike to just challenge and space around quick attack more, and allow for easier combos as well. Increased speed of jab2 coming out now makes the use of jab safer as a ground spacing tool. Dtilt and grabs still have a lot of reward. SideB coming out sooner just aids recovery mixups that much more. Dash attack and ftilt changes add 2 more viable random killing moves. Pika has to work hard in securing early kills, or it's just going to be a pain for him. Many of Pika's kills are read-based, so getting hard punished now isn't so great for him.
Quick attack still disrupts his spacing and the disjointedness of dtilt, utilt, and uair are still great tools, but Pika just has to be much more careful since Ike can keep up in 1 hit for every 2-3 of Pika's. Also, the new hitbox of fair makes thunder jolt in the air more dangerous since all of Ike's aerials and dash attack just goes right through it.
I could definitely see Ike having the advantage, but I'm wary that the counterplay at high-top levels just makes it even or something. Ike shouldn't have any issues with custom pikachu, either. Close combat helps avoid landing traps into heavy skull bash. Close combat can also go through projectiles. Pika also dies if he's hit by tempest during quick attack offstage.