There are much worse ways for a RAID controller to fail than suddenly not doing anything. What if it doesn’t notice it has failed and continues to write to a subset of devices only? Great recipe for data corruption right there.
Bad RAID controller/HBA, CPU, RAM, Motherboard, PSU are all hardware failures that RAID does very little (if anything) to mitigate. One localised incident in any of them out could make all of your drives turn into magic smoke or bits go bad.
You cannot rely on that sort of setup for data security. It only really mitigates one relatively common hardware to push storage system uptime above 99.9%. That has a place in some scenarios where storage “only” being 99.9% available has a significant impact on total availability but you’d first have to demonstrate that that is the case.