"Wayne Dyer" wrote

Naturally the first thing that comes
to mind is oak wilt, but as I've never actually seen oak wilt

As a recent victim (and therefore somewhat experienced), I would say this
does not look like oak wilt to me, just normal spring drop-off. If the
leaf-out does not come as heavily as last year, esp. in light of recent
rains, you might should get an arborist to take a look, or carry some of the
leaves in to someone.