ARM isn't open source, RISC-V is. ARM going under Nvidia's control is like to be more tightly controlled than ARM simply licensing it to everyone, and that probably still will be less than RISC-V ISA's being available as open source. Thus, ARM being under tight control will probably stifle innovation using this tech. Looking at Nvidia's business tactics, they are aggressive in trying to control and manage their market, and make it difficult for contenders to enter with a variety of proprietary layers and cost barriers. I imagine they would do the same with ARM, particularly as one of Softbank's rumoured reasons for selling may be related to profit from ARM - estimated 1.9 Billion USD last financial year up from 1.2 Billion in 2016, while Nvidia have tripled theirs in the same time frame. Not sure what AMD has to do with your or this argument.