alt Hacker News> a zero-day in the closed source firmware from Qualcomm will probably screw you anyway.
All the devices that GrapheneOS supports implement a clear separation of the baseband and the CPU in the form of SMMU, ARMs version of IOMMU. So a zero-day in the baseband does not immediately screw you - unless the code on the CPU side also contains vulnerabilities or there is a major flaw in the SMMU implementation that somehow breaks isolation.
Thanks for the clarification (and to the others that answered as well).
I probably explained myself in a shitty manner, I didn't try to downplay GrapheneOS efforts, and I should have kept my initial statement about "next best thing can create a false sense of completeness" as a generic remark and not specific to GrapheneOS, for which I don't have enough knowledge to know if it applies or not.