had actually put a U.S. style R&D system in place during WWII, and
instead of coming up with (however pretty they look on paper) dozens
of designs that never made it beyond wind tunnal designs and focused
on say two or three fighter designs.
For example, if they'd pushed through the first jet fighter design
in 1940 (I forget what it was called), and focused on incremental
improvmeents instead of always running to the next design.

Would this have had a major impact on WWII, or just drawn it out by
a few months?

They should have known what projects are the one's that are going to
succeed. What if the jet engine would have been a dead end and no FW-190 or
better versions of ME-109 would have not been developed?