Snapdragon flagships have solid security and it's the devices made with those which ruin it. Snapdragon has both advantages and disadvantages compared to Tensor.

Pixel 6 through Pixel 9a are essentially Exynos SoC devices using standard Cortex and Mali cores. Certain components are custom including a Trusty OS TEE and secure core, a separate hardened secure element chip, image processing, TPU for neural network acceleration, etc. Tensor was mostly standard Exynos. Pixel 10 moved away from Exynos other than the cellular radio chip, but it's not clear if that is good or bad for security. It gives them more independence, choices and control to an extent but they largely licensed the IP for the components and it's not necessarily more secure. Perhaps PowerVR GPUs have better security than Mali, but that's unclear. It does appear they got GPU virtualization support through it, but Qualcomm cares a lot about virtualization too especially since they support laptops with Windows, etc.

GrapheneOS have mentioned in the past that the Qualcomm baseband processors compare well to competition in terms of security and isolation support on their respective SoCs. There may be other aspects they need to catch up to Pixels on regarding security though (like the secure element, open-source TEE etc.).