That's true but from what I've read Laminar flow wings need to be perfect to work, and I mean perfect, dirt dust grass is enough to effect the laminar flow. I've never read anything other than a poor finish such as chipped paint causing issue's with elliptical wings which is true for every other type also.
Laminar flow 'exists' at approximately RN 500,000 - or just about taxi speed out of the chocks. Laminar Flow per se, never existed in any wing including P-51 45-100 series. That said, the Mustang wing did achieve 'Laminar Flow like' results in comparison to conventional NACA 23xxx wings - namely in delayed boundary layer separation. The region behind the BL separation is extremely turbulent, low energy flow which is a factor to increase friction drag.
Where the NAA High Speed/Low Drag excelled, was a.) extremely low profile drag due to the shape of the airfoil, b.) extended attached boundary layer before adverse pressure gradient caused separation - due to the aft location (relative to every conventional fighter with T/C max~ 25-30% Chord) of 37.5%, and c.) extreme care inproduction process relative to butt joints, small openings in the surfarce of the wing, sealed control surfaces, flush rivets, puttying/sanding and priming Leading Edge to 40% Chord. Additionally the ammo/gun bays were aft of Max chord Thickness. RAF ran some experiments at RAE to polish the surface and found little improved speed gain.
The lore of chipped paint and scuff marks are way overstated as detrimental to the Mustang wing. Obviously operating out of muddy airfields without some cleaning would be detrimental, but dirt/dust/grass was not a big issue.
Friction drag is what you are talking about, and three of the primary causes are a.) very grainy paint, b,) pan head rivets or poor countersink for flush rivets, c.) gaps in the wing skin - all of which tend to trip boundary layers 'before they should with reasonable production standards.
Elliptical wings optimize lift distribution and as such, reduce Induced drag due to the downwash.
Trapezoidal wings are 'nearly as good' depending on tip/root chord ratio - and far more easier to construct with consistency.
Flying at 10 feet was not any more deliterious (measurable) relative to friction drag than 500 feet. What is true however, is that Friction Drag is proportional to RN and will decrease for same velocity as altitude increases
drgondog has written a very thorough book on this plane's development, I weight his words more that I do yours.
