Im not saying that these should be removed (for obvious reasons) but that it could have been better made.
What would you have changed, then?
Zenith being overpowered is very much intentional and kind of obvious. You have to beat moon lord several times to get it so it isn't designed to help you beat bosses you've already defeated (unless you want to bump up the difficulty and go to expert/master/for the worthy or something). I don't have an issue with that.
Personally, what I have an issue with is the fact that it becomes the best weapon for
every class. That isn't really fun. Mage, ranged, and summoner have some really fun weapons at endgame but none of them come close to Zenith even when using your own armor type. For summoner that's not as bad since you are only replacing whips (and summoners sometimes use non-summoner weapons anyways) and your pets are still strong, but for the rest this is just... bad. It feels bad.
While we could nerf Zenith, I don't really think that's the solution. Just add new weapons for rangers, mages, and summoners with ridiculously complex crafting trees that are similarly powerful, at least to the extent that it's better than Zenith when you are using your correct armor type.
But... that's just my opinion.
As for "post-golem" weapons, I don't really have an issue with that. Things like Duke Fishron used to be endgame content after Golem. You can choose to do Duke Fishron after Golem and the weapons will be relevant, or you can choose to use more OP weapons and trivialize the fight because it's really hard. That's ok. That's the way Terraria has been designed. Optional fights are just that--optional. You can do them if you want or just skip them until later (or ever) because they are hard. Same thing with the events.
All of this said, the game is going to be as challenging/relevant as you choose to make it. If you want Duke Fishron's weapons to be relevant, just do the boss after Golem. Yeah, it will be hard, but those weapons
will be useful on the pillar events. I can't say that I have a problem with how this is designed. I don't think Duke Fishron should be required, nor do I think their weapons need to be changed. But hey, that's just my opinion, too.