To senior developers,Is the art of software design being lost?

No. It simply isn't in the spotlight anymore. Same reason you don't hear about pottery much, but they still exist.

I don't think so. It might feel that way with an abundance of mobile/web developers, but I'd argue "the old way" of programming continues to exist in other niches. All the people who wrote the classic Linux coreutils are mostly maintaining the same stuff. Terry Davis and Andreas Kling are proof that incredible feats of software engineering can still be done, even if you've got to follow "the old way" to a T.