[defenestration]

Years ago, when we just founded our company, I asked an experienced CTO: 'In your experience, what is the most expensive thing to adjust later on?'. He said: 'Changes in your datamodel'. That advice worked out well. We spent extra time designing our datamodel and it saved us quite a lot of money / time on refactoring later.

So making schema discussions as concrete as possible with Excel together with business stakeholders sounds like a smart thing to do.