I, Mr. Intelligent Designer, can construct an army of photosynthesizing alchohol-burning armed robots that unleashed will eradicate all animalia. Or at least more than hold their own. (I'll call them zylons.) Why hasn't evolution? The evo hypothesis is that designer-free evolution can produce organizational entities as complex as me, as complex as mammalia -- why not plants that complex, when I -- with my intelligence -- can?
I think I hear your mother calling ...
Why should it have done so? I mean, I was just outside on my lunch break, and I don't know if you've noticed, but those plants are literally everywhere. You can't swing your arms without hitting a plant, so they sure look pretty successful to me - they already appear to be holding their own fairly well, despite the fact that they don't walk or talk or shoot lasers from their slimy man-killing tentacles...