Explain all the other times using a Pokèmon with an advantage would’ve been the best option yet he does the opposite.
In the case of "NOT" using Pikachu, maybe its because some executive meddling was like "NO, that's TOO MUCH Pikachu"
As for regards to his other Pokemon, I don't know outside of story reasons, I mean Litten wouldn't have been good against Olivia and obviously Rockruff and Rowlet were chosen for obvious reasons. As Nanu, that was just Lycanroc story and for forcing the battle to be a 1 vs 3 hence why they made Tapu Bulu give Lycanroc the "sitrus" berry likely to chastise Nanu for being unreasonable (but I can't say for certain WHY the berry was given to Lycanroc for sure). And like I said for story (for past generations).
What we are talking about HERE however is something completely different.
I legitimately can't think of ANY real situation where Pikachu outclassed the Pokemon used against a certain powerful individual, that didn't capitalize on the opponent's weakness. For example I've never seen a situation where Ash used a grass type where the grass type was weak to said Pokemon but said opponent's Pokemon was super weak against Pikachu, and it wasn't A normal battle battle, it was against a super powerful opponent.
The closest I can think of which is contrary to the argument against this is Winona but Ash DID use Pikachu but it lost (same with Skyla).
But I don't recall an instance where Pikachu was Ash's strongest Pokemon, and the Pokemon Ash used instead was at a severe or moderate disadvantage where Ash was stupid NOT to use Pikachu. Look at his team: Lycanroc is both weak and super effective against Golisopod, but unlikely to do much. Golisopod outclasses Torracat. It's unlikely if Rowlet still has peck it's going to be that effective (so neutral at best), and Meltan while reasonable, just doesn't have much of a movepool, and Ash would be an idiot to use Meltan over Pikachu. The only advantage Meltan has is that it resists bug type moves.
I just legitimately cannot see ANY reason why Ash would use ANY other Pokemon against Golisopod. If it was ANY other bug type Pokemon I'd understand, but Golisopod, the one bug Pokemon that's weak to Pikachu? Not sure I understand anyone's logic there.
