These proof checkers all have bugs, every single one, and since AI is still 100% incapable of understanding simple mathematics we should assume agents are likely to cheat by exploiting a kernel bug. So a human really does have to be able to read and understand the proof. There's no difference between blindly trusting Lean and blindly trusting Grigori Perelman: yes you can be reasonably confident the proof is correct. But you gotta check.

This future of "the AI built the compiler and it's totally incomprehensible spaghetti, but don't worry, it verified the compiler works using this AI-generated proof assistant whose codebase is also pure spaghetti" terrifies me.