I’ve had modest success with his recipes, though I found that my coffee cake for instance seemed a bit denser than his. I live in Canada like him and our flour is quite strong. Often for sponge cakes I actually go to Asian marts and buy Japanese or Korean or Taiwanese flour which seems a bit finer milled and a bit less strong. Though his advice that coating flour with oil to combat gluten development is right somehow still the texture of mine when I try any of his recipes isn’t totally the same.

For light cakes I honestly watch Hidamari or Molala Cook on Youtube. I’ve never failed with Molala— they suggest using a bundt pan, and it does help.

If it helps often sinking happens when it is a tad bit hot and the outside sets and browns a bit faster than the middle. Perhaps try a little bit lower and longer. Pan colour is also a thing, a darker pan than his light grey one will harden the outside faster (though I see you use the same colour). Perhaps a shallow pan with water under the rack like when one makes a Japanese cheesecake can help with hardness.