Our of curiosity, which specific MS product is the one you see as most valuable / hardest to do without for IT security?
I can't imagine it's word or excel or anything document-centric. That's what most people think of when they think of MS Office, but in this day and age there are plenty of totally servicable alternatives.
You'll be surprised. Company documents are usually all made in the shitty format that only really works in MS Office.
And of course MSO doesn't even provide .NET components so someone could create a converter tools using MSO, you have to work around it or use Libre Office's soffice command, which provides limited support for proprietary MSO features. Don't tell me that's not on purpose.