I don’t have many memories of the third Sams book. I think I had more pity for Martin than for his father, because kids being bullied was relatable, whereas adults who were bullied looked weird and even contemptuous to me. But at the same time, I think both Martin and his father were self-inserts, and Paul Maar just is a better adult than kid. Or maybe he just had forgotten about being a kid.
For a superpowered nerd kid, read HPMOR if you can stand the smugness, or any other litrpg. The Neverending Story also fits the bill.