Then look at Black's arc which can be summed up as Goku and friends getting beat up, leaving, getting beat up again, etc.
This is a gross oversimplification of that arc. You could literally say something similar about almost every arc. In the Namek Arc "They are just beating up Freeza's henchmen until Freeza shows up." They are fighting his henchman and outside of the Dragon Balls there really isn't that much else going on. Yes, I do consider it to be the best arc in the franchise myself, but I also consider the Zamasu arc to be right up there with it.
they made them feel like events compared to the Goku and Vegeta show Super gave us
I see that as a natural development of the characters. Goku and Vegeta are the pure-blooded Saiyan warriors who devote their life to fighting, they should be by far the strongest and the ones to take on any oncoming threats. Besides, how the "Goku and Vegeta show" was avoided in DBZ is that the cast was literally left waiting for Goku every single time. It became a trope that happened with ridiculous frequency to the point where it became very predictable and boring. The usefulness of the rest of the cast literally stops as soon as Goku shows up. Outside of the fight vs Vegeta in the Saiyan arc, everyone's usefulness constitutes holding down the fort until Goku shows up. I would take a "Goku and Vegeta show" over a "wait for Goku show" any day of the week. Now, don't get me wrong, I think that DBZ is better but they certainly are on the same level and I think it is strange to sit here and say that they aren't in the same league.
lackluster Black arc is as good as the Namek or Cell arcs ?
I don't consider it better but I consider it to be pretty damn close. The Cell and Namek arcs are the two best arcs in the franchise to me and the Zamasu arc is right up there with them. If it wasn't for the poor ending and how Trunks's power scaling was handled, I would consider it the best arc in the franchise to be quite frank with you. It gave us a villain with a nuanced character and legitimate motivations for the first time ever rather than a generic evil guy every single damn time. It featured somebody other than Goku or Gohan being integral in the defeat of the main villain(even if Trunks had some strange moments.)
DBS features characters receiving power boosts that are ultimately more interesting and nuanced than "I spent X amount of time training." Three of Vegeta's moments where he gained huge power boosts are a reflection of his improvements in character and actually had meaning further than "yeah I totally punched the air for a year in that chamber." Aside from the two rage-induced transformations, it pretty much always comes down to spending more time training in DBZ. Generally speaking, Super Vegeta as a character is by far my favorite iteration of Vegeta and without it I would have been stuck with the garbage that is Buu arc Vegeta.
The fights are just flat out better and more interesting in Super. They have fights that aren't strictly decided by power, have more fights that aren't complete domination by one side, and feature generally more dynamic fights. Additionally, unlike DBZ, they have fights with interesting clashes in ideals and motivations rather than just being a clash of fists.
Like I said, I consider DBZ to be slightly better, but they are more or less on the same level with DB being significantly above both of them.