MS Office (specifically Excel) is not a shitty product. There's a reason why it has a larger monopoly with finance types Wall Street than Google does with search. Power users can quickly build powerful financial models with it.
Doing complex modelling in Excel is not a good idea. There is no way to do proper software engineering, so bugs are common and hard to find. For examples, see http://www.eusprig.org/horror-stories.htm
Many great projects start out as excel spreadsheets: someone has a problem, solves it with excel, then goes on to solve other problems with that spreadsheet. People use it and become dependent on it, but over time the thing becomes intractable.
At that point in time, the functionality of the spreadsheet gets implemented by actual developers into some "engineered application."
If you are suggesting to NOT start with excel, then propose another solution-- but good luck getting anyone to use it. The key thing is, no one wants to engage "software engineers $$$" to solve a problem that lands on their desk which they handle by themselves.