All Nordic chips are susceptible to bootloader attacks which make them a poor choice for storing key material. This can be mitigated in the design phase by adding an external security chip like a ATECC608B but if you were to tear down a device and see a board present without this module it certainly will have other vulnerabilities too.
Having worked extensively with both Nordic and Chinese chips, what makes Nordic win is the ease of development - they are by far the best in market when it comes to programmability. Hands down.
The security problems have been known since the NRF51 and despite that those vulnerabilities were carried over into the NRF52 because the cost of validation of chip designs is so prohibitive they did not want to touch it and filed the “oh some random person can extract the entire contents of the chip” bug as “won’t fix”. They are baked into a silicon ip core and can’t be fixed with a software update.
As for RISC-V, there are some amazingly innovative and brilliant alternatives to TrustZone presented at the conference but I suspect Rambus may block innovation here using their position on the board (and chairing the security standing committee) in favor of their own (patented) solutions using an embrace, extend, extinguish strategy.