> This wasn't true when Office was first introduced and Office still created a domineering market share

It was absolutely true at that time, but Microsoft was already a behemoth monopoly with deep customer connections throughout enterprise and was uniquely positioned to overcome the moats of their otherwise fairly secure competitors, whose users were just as loyal then as the GP is describing about users now.

Even if OpenAI could establish some kind of moat, office applications make for very poor analogy as to how they might or whether they need to.