The issue is with the well-being of the tech ecosystem and less with SoftBank or ARM's well-being as a business. SoftBank may not have contributed to ARM's success, but their neutrality allows ARM to license their IP without the kind of self-dealing you would get if Nvidia owns it. Further, Nvidia has a poor track record in global citizenship.

The net result is that the overall ecosystem is going towards a degenerative state, rather than fostering innovation and diversity in tech.