As you climb the engineering IC ladder your responsibilities involve larger and larger tasks and timescales. It's not possible to measure whether someone can make the right decisions about the architecture of a service as requirements change over years in a 1-day interview. Anything that isn't "be the engineer maintaining this service for 1 year" is going to be a proxy for that, which can be learned and gamed.

What would be a "proper" interview in your opinion?