To capture both characteristics (spoke too long and sloughed over the easy stuff), I suggest:
The lecturer relied on long-winded hand-waving.
If the phrase necessarily has to stand for the person, I suggest
The lecturer was a hand-waving windbag.
Tediously long in speaking or writing m-w
An exhaustively talkative person m-w
hand-waving (n., adj.)
The action of waving or gesturing with one's hands; an instance of
this. Frequently in extended use: the use of gestures, insubstantial
language, or unsupported assertions in order to convince or impress.
Also written handwaving. In formal conversation / speech omitting
important details about the subject matter either because 1) the
audience is perceived to be ignorant 2) the speaker themselves is not
well-informed on the subject matter or 3) a little from column A and a
little from column B. urbandictionary.com
If the presentation is too long-winded, the discussion leader
should attempt to summarise it by emphasising the key elements
contained within it. Josh Moust et al.; Introduction to Problem-Based
There was a bit of chuckling, and Mr. Maurer objected to the seemingly
long winded answers as Connolly stood, seemingly pondering a way to
tailor his questions to elicit direct answer. J. M. Carter; Johnny
Even today, with all out sophistication, many explanations of the
results from scientific data are little more than what is often
labeled as "hand waving." I have sat through research-group
meeting listening to one person pontificate at great length on why we
are getting a particular results, only to have me or another person in
the room point out that the data actually show just the opposite...
C. L. Parkinson; Coming Climate Crisis?