I have to disagree. There are many areas where things are extremely deterministic, regulated financial services being one of those areas. As one example of zillions, look at something like Bond Math. All of it is very well defined, all the way down to what calendar model you will you use (360/30 or what have you), rounding, etc. It's all extremely well defined specifically so you can get apple to apple comparisons in the market place.

The same applies to my checkbook, and many other areas of either calculating actuals or where future state is well defined by a model.

That said, there can be a statistical aspect to any spreadsheet model. Obviously. But not all spreadsheets are statistical, and therein lies the rub. If an LLM wants to hallucinate a 9,000 day yearly calendar because it confuses our notion of a year with one of the outer planets, that falls well within probability, but not within determinism following well define rules.

The other side of the issue is LLMs trained on the Internet. What are the chances that Claude or whatever is going to make a change based on a widely prevalent but incorrect spreadsheet it found on some random corner of the Internet? Do I want Claude breaking my well-honed spreadsheet because Floyd in Nebraska counted sheep wrong in a spreadsheet he uploaded and forgot about 5 years ago, and Claude found it relevant?