I think they are both great defenders. It takes a lot of skill to be able to enter into someone's wheelhouse and make them miss consistently, which is what both are excellent at. To me, it's harder than staying on the outside and moving. In regard to who is better, I think it is Lomachenko. He is more versatile. He is slippery inside but has significantly better feet than Alvarez.
How does that answer the OP? Canelo lost to slow Golovkin, he also eats more punches than Lomachenko. Clen already lost to slow Golovkin.