> Of course Lean proofs are rarely a good way to understand proofs, but hopefully they can be used to generate more human understandable arguments.

I would object to the first part: Of course there is a nontrivial learning curve, but then I'd argue that non-slop Lean/Agda/Rocq/... formalizations are amazing for understanding proofs. A good formalization presents the outline and the key arguments in nicely structured form, and then, unlike pen-and-paper proofs, also allow you to get the details on every single step, exactly to your desired level of depth.

The proofs in Martín Escardó's TypeTopology Agda repository come immediately to my mind as an example. [An interactive Agda tutorial is here: lets-play-agda.quasicoherent.io]

In contrast, LLM-generated formalizations can currently be extremely messy. They certify truth and can also contain interesting arguments, but substantial work is required to bring them into a shape that contributes to the actual goal of improving our understanding of the mathematical landscape.