Depends on where you want to be...
IBM sells a tiny number of mainframes - compared to WinTel servers, but it makes a large profit on this business. I suspect that IBM are wanting to establish a similar business in cloud, so let MS and AWS slug it out at the commodity end.
The only question is whether IBM can convince (enterprise) customers of the tangible added value of their cloud offering over commodity. But then I suspect neither Azure or AWS will let you run OS/390 applications...
Biting the hand that feeds IT
