@leusee he's not even conscious, and i wouldn't call it bs after poison hand immortal butterfly lady, godzilla bugs and whyever the hunters have such inhuman fighting potential as hinted at and also the omniyoji
this is also an explanation of and was hinted at by the mc's ridiculous strength( which everyone was amazed by and moon boy might've actually figured something out from, hence his confidence)
which i always thought would lead to more
and him mastering his traits is what is the point here, first he got swordsmanship,
now he might get control over his already massive strength( which now notably mostly happens when he's trying to save someone or he's in real danger and he intensely tries to use it), which might also shed more actual light on the mysteries of this illogical world,
i think keeping it fresh is important and this gives him a realistic way to get stronger without odd zenkai boosts or taking away from the fact that he was already pretty strong and interesting, he'll still be using a sword so it wasn't useless the training
it also would explain him surviving the poison and it adds more intrigue and more plot potential to our mc that isn't just him repeating the same thing,
I understand why you'd think it's a bad thing
but this was more a sudden plot twist with real foreshadowing and less of a power-up considering he was already half-dead and is now just a mindless beast drawn to action by thought presumably.
it's incorporated well and hopefully won't be repeated much more among the main cast, so it's fine, the super saiyan was amazing but still just a sudden transformation remember?
this isn't as perfect as that but it's still well written, foreshadowed and intriguing, there was even a light scary foreshadowing with him changing faces and grinning
It also adds a layer of mystery and value to our mc himself, like does the dad know? Is the mother where he got it from?
The design of course is quite good as well, with his spindly hair being incorporated and the mc was always an oddball, so if anyone's secretly gonna be part mythical being....