There happened aThis is an example of subject/verb inversion, not thea case of ellipsis as you said. weWe use this kind of inversion while comparing subjects of the verb and not normally the objects. We call it inversion in comparatives as in
Paul is more interested in Maths than is Mary.
You play golf better than do I.
So in thethis sentence, there is no ellipsis of the subject. SubjectThe subject is actually there after is which is the knowledge born of experience. Actually more simplea simpler way to write what is there in your example is
... more measurable than the knowledge born of experience is