If you're talking meta archievements, yes it is optional. if you want to do more than that you _need_ to actually FINISH the kitten tower for serveral archievements to finish. If you are a completionist in any sense, its mandatory to you.
That aside, it is just not fun. It is glitchy, laggy, it wastes more time with waiting and its intro cinematic than it gives you gameplay-wise, it needs a rework.
On top of that it is disproportionately difficult, partly due to the bad code, partly due to design choices, compared to any other JP in the game, and I have done them all, bar this one.
Edit: "You dont need it" is also a very poor defense for something that, to quote Marie Kondo here, does not spark joy. This is a game, not a chore.