Formulas are foundational and arguably the reason spreadsheet software exists in the first place (automating calculations), everything else in a spreadsheet application is arguably entirely an attempt to make formulas easier to work with.

As an example, Pivot Tables are an attempt at an "easier" UX for a very common sort of (set of) formulas: What is the "summary" here? What does this table look like "sideways", and is that a useful summary? (I've seen spreadsheets with manually built pivot tables in hideous formulas. Pivot tables really are easier than that mess.)

Formulas are what a spreadsheet user comes to a spreadsheet for. So most of the complexity of the spreadsheet "has to be there" for people to consider it a working spreadsheet.

That's a big source of friction for me as a developer because I know when someone asks "Can you make it more like Excel?" they don't mean "can you make an uglier data grid here" they more often really mean "how interested are you in rebuilding Excel's formulas engine, it's charts engine, and maybe it's pivot tables system, and a few other things I regularly use?" but they don't know that they mean it (because they don't understand themselves the tools they use, they just use them). Raw rectangular data grids aren't actually a very useful user experience, and a lot of users ask for them because they are familiar, but also a lot of them ask for them because they've got a head full of unchallenged assumptions that "computers are math machines, I should be able to just insert a formula here" without realizing it. More often than not when a user is asking me "Can you make it look more like Excel?" it's that there is some formula they want to run and asking the follow up questions what formula they think that is is often more interesting/useful than "make it look more like Excel" ever is. At least in my experience.