RISC-V is coming for ARM's market, and it knows that it's days are numbered.
It's a long-term threat. Right now, ARM enjoys a lock on the phone market, deep penetration into self-driving and robotics SoCs, and is the only viable cloud alternative to x86. That's not a bad position to be in.
ARM's main problem is that its business model hasn't supported the kind of revenue levels that traditional chip companies have garnered. That's why it's suing Qualcomm over Nuvia's architectural license, in order to try and extract royalties from its downstream customers. It's a "Hail Mary", but if ARM were to prevail, it'd be huge for them (in the short/medium term, anyway).
Its second problem is longer-term: the way its patents have been shown to be vulnerable to exploitation by governments engaged in trade disputes and security concerns. That was a really bad precedent, and I wish ARM had sued the US to get it overturned. I'm sure that put China and many others off the idea of using ARM-based CPUs for their critical industries and infrastructure.
Unfortunately, the Qualcomm/Nuvia lawsuit has poured cold water on any US-based firms introducing new ARM ISA CPUs (chiefly Intel & AMD), after the patent/trade dispute already turned off foreign firms and governments from jumping on the ARM bandwagon.
So, I agree that the brightest days of the ARM ISA are possibly behind it, but not because RISC-V is actually better. Mostly due to business and trade reasons. I've seen no technical analysis which supported the idea that RISC-V is better than AArch64.
BTW, ARM can always pivot and get into the RISC-V IP market. It probably wouldn't be as lucrative for them, but as long as they have the expertise and there's money to be made, it should remain an option.