Nobody used terms like "can't beat" so I have no idea why you brought that up.
My reasoning is also far from fallacious - it's generally not plausible to assume that a worse character beats the better character unless there's some specific reasoning provided [which already isn't the case in the Pikachu vs Bayonetta matchup]. A better character is better -and wins more matchups- for specific reasons and these reasons ultimately play a role in
any matchup. Bayonetta is a better character than Pikachu because she has better, more consistent damage output, more range on her neutrals and because she's not held back as much as Pikachu by an utter incapability of getting KOs. That makes her a better character than Pikachu.
But these are the same reasons that make it plausible to assume that Pikachu doesn't just have the advantage in a direct confrontation against Bayonetta. It is not a plausible assumption and it's necessary to point out what exactly allows Pikachu to mitigate his shortcomings as a character specifically against Bayonetta when her character traits are generally superior.
Nobody has ever provided a good reason why the matchup is supposed to be in Pikachu's favor nor do results imply as much in any way. Would it be plausible to assume that Greninja beats Diddy Kong just because somebody claims it is? When results lean towards an evenish matchup? We have a 2-2 record between Pikachu and Bayonetta for now and all observable data tell us that Bayonetta is overall a stronger character. There's
no logic that could reasonably lead us to the conclusion that Pikachu wins this. It's absolutely implausible to assume so.
And Bayonetta being the better character
of course has a lot to do with it.