You’re begging the question by assuming Microsoft’s market position hasn’t been artificially inflated with anti-competitive measures.
When you already have a dominant position in one market – say, office productivity software or operating systems – leveraging it to push another product below cost to effectively take over another market actually would (and in the past, literally has) put MS in hot water with US antitrust regulators, so it’s not that hard to imagine that, depending on how they did it, this might also run afoul of antitrust regulations.
The crux here would seem to be whether MS is really “hiding the true cost of Teams from enterprise customers.” They’re likely breaking the law if they are.