Mert

That is the cost precisely. A single formula has no observable middle, so every fault is at the same address.

Defending helper columns properly, since they get treated as a failure.

I inherited a sheet where somebody had collapsed everything into one enormous expression. It was correct, it was impressive, and nobody could change it, so the team maintained a second sheet beside it. That is worse than fifteen helper columns.

The test I use: could a competent colleague modify this without asking me? If not, break it up and label the pieces. A sheet is a document as much as a program.