That's a good point and you're right. The hotter the fire or the more fuel that's required to maintain a pit temperature, the less smoldering you get which is where most of the smoke comes from. I have found that 250 and below for smoking on a pellet cooker to be the sweet spot. However even will cooking hotter than that, for example grilling - I've still noticed a nice subtle smokiness to pretty much anything I've cooked.
I'd give my nod to Yoder and Woodmaster. I've owned pellet cookers from both and they both produced a nice smoke ring with a great flavor.