That is going to put a dent in ARMs revenue. Even if that particular chip isn't a big seller, it means ST now has a drop-in replacement for ARM in their other SoCs. Soon people will realize that ISA is often irrelevant, but the peripherals, libraries, and tools are.
Any ISA can be dissected, but ultimately RISC-V's got the mindshare and the license.
There's no solution, only tradeoffs.
That's one opinion. Another ARM engineer who contributed one heck of a lot more to ARM's success (designed ARM7TDMI, Thumb, Thumb2) says RISC-V is great. See at 51 minutes in this https://www.youtube.com/watch?v=_6sh097Dk5k
That's not ST, it's by the Chinese company GigaDevice that makes (decent) clones of the STM32 series. Your point still stands though.