In gorgrond its pretty clear that magic exists which can convert plant life into living enemies.
Its common sense that trees can be regrown and are a valuable resource.
Many takes on the warsong vs. sentinels is that the warsong are invaders stealing cultivated resources. But what if the nightelves were aware of the possible villains they are allowing to suck azeroths energy, just waiting to be infused with the everblooms magic, but its only at the higher level. Meaning the common night elf thinks they are protecting a majestic forest while the higher ups, more specifically upper ranks of queldorei / moonguard know they are just growing super weapons waiting to be infused with damaging magics?
Ehh… Two points. First: The plantlife on Draenor is very different from that on Azeroth. The Primals are not simply “overgrown nature” but rather the greatly diminished offspring of the long-dead Sporemounds. Which, (oversimplifying) were sort of like the life-equivalent of elemental gods. Azeroth has never had such beings, nor would the plantlife ever develop into Primals/Sporemounds.
Second: The Warsong Clan were from Nagrand. Their primary adversaries were the Gorian Ogres. Your theory would be a lot more poignant if we were talking about the Blackrock or Dragonmaw clans, who were from Gorgrond and would have been constantly at odds with the Primals.
To put it bluntly, the Warsong were simply the most war-like clan and had no reason to respect trees as the Night Elves do. Thrall sent their clan north with the task of harvesting lumber for the construction of Orgrimmar. The Night Elves (obviously) defended their forest, Warsong went fel-crazy, Cenarius was killed, and the rest is history.
Right up there with “Should we start using child labor to preemptively halt America’s obesity epidemic?”, and “Feeding spoiled or poisoned food to orphans helps them understand that anything can have use.”
On a more serious note, the Warsong didn’t put that much thought into it beyond “See. Want. Take.” It was…well, this:
Besides, night elves already had treants and forest ancients with them. It’s not like they didn’t already have ways to utilize the forest as a weapon.