It's really not as clear as people think, and as a person who thinks Zama should be unbanned I disagree with this.
Zama is strong with a base 130 attack stat yeah. However, it gets no boosting item and only has howl to boost it's attack stat. So while it can deal some good damage to offense, it does have ways for offense to beat it.
Many other posts point out the ways offense can adapt to Zama but I'm just gonna repeat them. Volcarona turns Zama into set up fodder. If Zama stays in and howls to try and kill it with Wild Charge, it also risks getting burned which makes Zama dead weight. Grassy/Electric seed Hawlucha always lives a wild charge from Zama, gets an SD, and proceeds to kill Zama in return. Zama is also pretty prone to taking chip throughout the game, so mons like Tapu Koko and Dragapult can outspeed and kill a weakened Zama. Landorus and Garchomp also handle Zama well, IF it's not running ice fang, and deal good damage in return to make sure another teammate could come in and revenge kill it. Specifically Landorus, who also can remove Zama's howl boost with Intimidate. This is a more niche pick BUT, banded Buzzwole is an offensive mon that just completely destroys Zama. Aegislash is another more niche pick that also deals with Zama, though it depends on the Aegislash variant.
As someone who used
this team for a fair amount of games to try and get reqs, I never struggled with Zama. This struggle that people have with Offense vs. Zama is more of an on paper thing than in practice. At least in my eyes