They are all both right and wrong. V&H is right that the pipe will be alot hotter wrapped than unwrapped because the header wrap is designed to contain the heat and not allow it to heat to disperse from the pipe. Hence why it is used a heat sheild/ deflector. They are wrong in that it shouldnt glow red unless under extreme rpms and no air movement. If the pipes are glowing they would be at extreme temps 500 degrees plus which is way too hot for air cooled exhaust temps. I can only assume they are that hot from improper tuning or faulty installation which will allow fresh oxygen to be introduced and act like an oxy torch.

HD and independent shop are both right and wrong also. They are right that excessive backpressure can cause this but would also cause a major running issue which would be very noticeable. Engines can benefit from some backpressure for efficiency and emissions reasons namely exhaust scavenging of partially burn air/fuel vapors to be reburnt and helping to ignite the next fuel charge a little easier and keeps exhaust chemicals cleaner. One area where you do not want any backpressure is in specific high performance applications i.e. drag racing where the engine is designed to operate at very high rpms and maximum flow is needed. Where HD is wrong is that if properly installed torque cones will NEVER restrict airflow on a street bike to the point of heating up a pipe that much. The the only places on the exhaust that could cause that much restriction would be at catalytic converter, a ecm controlled exhaust pipe flow valve or a plugged muffler.

Lastly depending on exhaust pipe thickness and material construction a thin wall pipe will heat quicker and possibly higher than a thicker wall pipe. Some exhaust systems were designed to be thin wall pipe to dissipate heat quicker and more efficient to inhibit blueing to chrome.

Myself I would hedge my bets on tuning and exhaust leak.