"top 100 anime moments where bullies got what they deserved"
It really isn't though, because we got multiple episodes and hundreds of lines that are dedicated to the psychological damage this has caused him even now as Rudeus, he suffers from it, and talking to Man-God always reminds him of his "ugly body" and his past.The way it's done in Mushoku is like "btw Rudy had cancer LULZ".
While the "revenge" part might be important for you, it really isn't for this show nor for most people in general, not even for the bullied themselves sometimes.
For all we know they could have been punished but that didn't change anything.
For all we know MC didn't help to get them punished and the only things his parents know is that he got bullied etc. etc.
It's up to the imagination, it doesn't mean they make fun of the matter, it just doesn't serve as a story telling device anymore or rather, it serves a different purpose to those anime that use it for a "revenge-story".