They are not suing them to use "inferior designs," you're completely misrepresenting the issue. They are suing them over IP and contract violations. The ISA in

They are not suing them to use "inferior designs," you're completely misrepresenting the issue. They are suing them over IP and contract violations. The ISA in question is irrelevant here, you could also get sued by SiFive if you licensed their cores and then did something that SiFive believed violated that license. It's not that deep.