Any ordinary well-designed microkernel gives you a huge benefit: process isolation of core services and drivers. That means that even in the case of an insecure and unverified driver, you still have reasonable expectations of security. There was an analysis of Linux CVE's a while back and the vast majority of critical Linux CVEs to that date would either be eliminated or mitigated below critical level just by using a basic microkernel architecture (not even a verified microkernel). Only 4% would have remained critical.
https://microkerneldude.org/2018/08/23/microkernels-really-d...
The benefit of a verified microkernel like SeL4 is merely an incremental one over a basic microkernel like L4, capable of capturing that last 4% and further mitigating others. You get more reliable guarantees regarding process isolation, but architecturally it's not much different from L4. There's a little bit of clunkiness for writing userpace drivers for SeL4 that you wouldn't have for L4. That's what the LionsOS project is aiming to fix.