Not sure about the stems but certainly some strains respond better to the technique. My Hawaiin Skunk Haze is much more uniform than the Critical Haze. My second grow was two mainlined to 8 Critical Kush/hempy/600w from clone that unfortunately the police got not long after this pic @ 3-4 wks flowering
And then I had two C99 Xline 32 mainline outdoor from seed(pics gone on old riu), so this is my 3rd mainline grow and 4th grow total.
According to Nugbuckets
"Some strains are better suited than others for the main-lining method. The best strains for main-lining display "single cola dominance," which means that it tends to grow in the class "Christmas tree" shape of Indicas, Afghani strains, Kushes, etc.
Sativa dominant strains often do not grow in this shape, and tend to have lots of secondary branches naturally spring up. Clones also tend not display the same level of single cola dominance as plants grown directly from seeds. With that being said, main-lining can be used with all strains and even clones to optimize the nutrient distribution from the roots and create more balanced plants."