Anything Turing-complete is a powerful tool, but the reason people are reacting negatively is because of how much of the wrong tool it is.

• Does an excel-based solution offer adequate runtime performance? No
• Does an excel-based solution offer adequate write concurrency? No
• Does an excel-based solution offer appropriate data durability guarantees? No

Basically the only saving grace of Excel-based solutions is that they are built in tools that finance workers comprehend, and that is quite simply not enough. To base systems at this scale on Excel is criminally negligent.