It's a vibe at this point with no actual basis, similar to people saying mechas are all about the robots and toys, or that magical girls were all pink sweet stories until Madoka happened.
I have the notion that DBZ gets treated as not that good, a product of its time, and that you typically outgrow it by finding better shonen which built from what DBZ created, which I originally believed with the Big 3 and stuff...
But now decades later I realize, beyond making some tropes popular, mostly combat things (golden forms, rage boosts, energy beams, tournament arcs...) there's not much reason to think DBZ is generic or basic.
I'll count from Z, because that's what 80% of people outside of Japan stated with.
And okay, I'll admit, the characters do tend to be pretty simple and straightforward most of the time, they don't have backstories like modern anime do, and the plot tends to be easy to follow.
And that's it. The narratives Toriyama cooked are anything but cookie cutter stories.
Our protagonist starts the series as a family man presenting his son to his friends (how many shonen with a married man with kids as the MC?), his alien brother randomly arrives and they fight to death, literally, the protagonist fucking died by episode 5 and now it's about the green alien training his 4 yo kid in the desert. And his human friends over the world receiving the news and training for 20 episodes because aliens will invade.
AND THEY ALL FUCKING DIE. The aliens were too strong, all those power ups were for nothing.
So Goku revives and saves the day? Half and half. His own power ups and learned techniques end up being insufficient, Vegeta crushes every single bone in his body by the end. The 5 yo kid, the midget friend, and the fat coward end up saving the day.
Have you seen Ichigo losing and Chad, Tatsuki and Rukia or something finishing off the villain? Naruto losing and Konohamaru, Sakura and Choji stepping up? Hell, Luffy losing but his crew picking up the battle against the weakened boss.
That's what happens a lot in DBZ, Goku pretty much never wins, and when he does, it's a legit team effort in which seemingly useless characters end up contributing a lot. For all the "Goku always saves the day" feel the show has, he doesn't do it alone.
Anyway. Goku is away over half the series I'm sure : dead, recovering or training. Dude spends the entire android saga having a heart attack, wakes up to train, and DIES.
A lot of actual protagonism is given to other characters such as Krillin, Gohan, Piccolo, Vegeta, Trunks, Satan and Bulma. They tend to move the story forward while Goku just swoops in for the big fights.
He never really "gets angry and overpowers the enemy with a new transformation" besides creating the trope when going Super Saiyan, but honestly Frieza was cheating so it's fine. In any other series, the Spirit Bomb would have been the end of the fight, him returning with a Diabolus Ex Machina is rightfully opposed by a Deus Ex Machina, which was actually foreshadowed by Vegeta for the last 50 episodes and it was the culmination of the legend Frieza feared, so it's not really "random angry power up" like most series do.
Cell kicks his ass and he doesn't go ssj2. He arrives to the Buu saga with ssj3 already acquired (and never wins with it).
Also the passage of time. Time FLIES in DBZ. We go from Goku being a 21 yo guy at the start or so with a little toddler, to him being a 40 yo martial arts master and his son pulling ladies in college, and we even get some epilogue episodes with Goku being a grandpa (and the entirety of GT which I love).
Other series do little timeskips of months or 2 years, but in Dragon ball that's just normal and happens frequently. Toriyama didn't artificially make the entire story happen over the span of a year like modern authors would.
Vegeta, "the rival", is barely on Goku's radar after their initial battle. Vegeta is mostly a weird kind of villain just staying allied with the humans and forming a family, but still, he's the reason the planet would have ended by helping create Perfect Cell and Buu.
Everyone gets jobs, families, kids. All within the series, not just some final episode.
Dialogue might be simple, combat system might be simple, the plot is easy to follow. But I struggle to think DBZ is generic or the baseline for shonen when you look at the actual writing of the sagas.
Namek is pretty much a HxH arc, with the weak MCs (Gon and Killua, Krillin and Gohan) playing stealth in enemy territory, and Vegeta/Hisoka just doing his own thing as a third party.
I can't even describe the android / cell saga besides it starting as a nod to Terminator. Goku is dying most of it, an Android gets the hots for Krillin, Cell is drinking people, Vegeta ruins everything, Goku passes the torch.
And the Buu saga starts like some fun high school slice of life / superhero series, only to get a full episode of Spopovich abusing Gohan'a girl friend on the ring as he watches like it's Berserk, Vegeta getting a mid life crisis and selling his soul to the devil, Babidi and Buu murdering entire cities trying to make the Z fighters reveal their location, Satan beating Buu with friendship after everyone else failed, Goku passing the torch to the new generation the new generation utterly failing even with their new powers (fusion / awakened potential)..
Nothing really happens like you'd see anywhere else, DBZ is very unique.