Very roughly, and assuming mid-range is around 400-500 bucks like the fairphone:

- Memory tagging is still pixel exclusive for now, but it's part of ARMv9 so it should be available on more devices in the future unless they disable it

- Most devices now have a secure element, though the exact capabilities vary

- Baseband isolation - no idea really, most chipsets should support IOMMU (or SMMU as ARM calls it) but is not very obvious if that's setup sanely or even used at all on your average device. So I'm guessing most devices are about the same.

- Security patches certain vendors are much better (like Samsung, for their non-budget devices anyway) but a lot do much the same. It shouldn't generally be worse because of Google's requirements.

- Verified boot is pretty standard

Memory tagging isn't Pixel exclusive anymore. Fairphone doesn't lack baseband isolation since it's a standard Snapdragon feature. Fairphone is worse than many OEMs at providing the standard security features and patches. Repeatedly using publicly available signing keys meant for testing for signing their OS is one example which has hopefully been fully addressed for the latest device.