I see a different issue: Who is the builder.

We have liberal and permissive rules for licensing an aircraft that people
build for their own education or recreation. These rules are also permissive
on how the plane can be used. The rule says:

(g) Operating amateur built aircraft. Operating an aircraft the major
portion of which has been fabricated and assembled by persons who undertook
the construction project solely for their own education or recreation.

We have other rules for licensing an aircraft that was build for some other
purpose. Those rules include certification rules for manufacture and sale
and rules for several purposes in the experimental category (R&D, Showing
compliance, Crew training, Exhibition, Air Racing, Market Surveys, and
certified kits.

As I see it what is done at Epic and other professional build operations is
not so much a violation of the 51% rule but a violation of who is the
builder under that rule. The rule doesn't really say that you cannot make a
profit while getting educated and recreating. On the other hand being in
serial production this way could be taken as a violation.
There could be a person (or persons) at Epic who qualifies as the builder
and those persons could license the plane under the amateur built rules.
Having a purchaser who does little or no work sign off as such a builder is
a flagrant violation and should be grounds for refusing to license the
aircraft in this category.

I personally would apply the following liberal standard (which I think would
clean up the problem): If a person was physically present while the bulk of
the work was done even if his presence was limited to cheering on those who
actually hammered and sawed then he qualifies as a participant and could be
treated as the builder. If the work he was present for meets the 51% rule
than he can license the plane under these rules.