I wouldn't consider MS Office "entrenched" any more, at least for the under-30s crowd. Word has been largely replaced by Google Docs, and Excel is slowly being phased out in favour of far more powerful programming languages like Python and R (but is still definitely dominant; I bought an office key mainly for that one app). Outlook has been replaced by web-based services like Gmail.

I remember being surprised when a couple of older people I was building computers for asked me to put Office on them. There was only one guy I knew from my generation who still used it.