Correct

Natural selection happens at the genotype level, not the individual level. Having a species that likes to combat with other individuals with, essentially, the exact same genotype, at the expense of both individuals, is often not a winning strategy.

(There are exceptions and caveats of course -- e.g. competition between individuals to select the fittest ones of them to preferentially survive, or Fisher's Principle which explains why the ratio of males to females is roughly 50:50 in most species, even though that's often not optimal for the species as a whole).

And isn't it advantageous to the whole forest if the mature trees are the same height? Doesn't that happen naturally all over the place? Something about equal sunlight, hydraulic pressure, hydration, and... I forget.

Man, that's some crazy logic. I'll take occams razor and state that wind movement abrades the leaves/limbs on one another.