Have you heard this one before

"I guess it depends on the bike and kind of riding you will be doing".
I installed Rinehart TDs on my 2005 SEEG with SERT tuned 103" motor. My experience is the long-stroke 103" motor more than makes up for any lost torque that might occur at the lower RPM range (1K - 2,500). Where the Rinehart TDs really shine over the other systems I've tried, and is where I feel baggers needs it most, is in the 2.5K to 5K+ rpm range. This is the range where passing vehicles @ hwy speeds or going up a long grade becomes quite noticeable. This is where the Rinehart exhaust system come alive.
I'm not saying your dealers are wrong... I'm not familiar with Rinehart TDs on standard displacement or even big-bore engines, and any loss of torque at low rpm might be an issue here... Regardless of displacement you must use a SERT or other tuning device to realize the performance gains in the upper RPM range. Before my SERT the Rinehart's at higher RPM were just OK...
I have some recent real world experience... I replaced my Rinehart TDs for SPO mufflers/V&H TDs before a ride last weekend to Laughlin for the Annual River Run. This is about 900 mile round trip test. The results confirmed the loss of higher rpm performance that is quite apparent based on my SOTP dynometer testing. There was a noteable drop off in the 2.5k - 4.5k rpm range and I found myself downshifting much more often with the SPO/V&H compared to the Rinehart. Any difference at the lower range RPM was negligible, where I think the stepped headpipe design has less impact. Again, this is SOTP and your results may very...
I'm keeping the SPOs cause I love the sound, but the cost is less roll-on performance at the higher rpm range. Everyone has to have their sweet spot...