With baffles you usually gain low rpm torque at the expense of high rpm horsepower. The restricted exhaust causes that. Depends on which way you like it as far as performance. I do a lot more riding under 5K rpm than I do above, so I like the torque. Plus the Dragsters are really loud with no baffles. I've not had them but I had a set of Speedsters which are about the same but longer.
Less/little back pressure gives more bottom end torque , the correct amount of back pressure give more top end horsepower. Baffles aren't always sized correctly for optimum performance. I've got $1250 titanium cans on another bike , but the cores were too big , I made restrictors for them and nailed it the first try , half way between the diameters of the new titanium cans and my previous carbon fiber cans. I've been modifying pipes and silencers since I was a teenager on both 2 and 4 stroke bikes. Then of course I had to start all over with my Power Commander IIIr. When I can't get on my buddy's dyno I use a G-Tech meter.
What you guys are saying is exactly what I used to think, little to no back pressure increases low end torque. But if you read Suzuki's info on the SET valve, it supposedly closes more at low rpm to increase torque and opens at higher rpms to increase horsepower. I really think the purpose of it is to reduce the exhaust level (decibles) so they can meet standards, and maybe the way they described the SET operation is just to cover up the real purpose.
I know I used to think you needed a little back pressure so you didn't over scavenge the cylinder and suck unburned fuel out the exhaust.
And I just thought of something else. Not that I've forgotten a heck of a lot of stuff over the years, which is true. It's not so much back pressure that you're changing, it's the exhaust velocity. You need high velocity, which can be hard to get in a large diameter pipe without having turbulence in the flow. A baffle, or pipe reducer, can improve that flow to increase low end torque. The balance is in getting a good flow velocity at both low and high rpms.