Life is weapons escalation. This holds as true for a plant's excreted toxic resins or a deer's better antler design or a skunk's more noxious skunk gland spray as it does for a human's Star Destroyer or Colt Peacemaker. Something, somewhere, will develop a way of getting around the defense to get at what it wants. Any species that expends its energy in weapons development while shortchanging eating, excreting, and reproducing is going to become extinct. Any weapon system that makes too big a drain on the creature's resources will cause its eventual extinction.
Specialists are more efficient.
Specialists let the thurka tree provide for all their needs, and thus conserve the energy trial and error require. Generalists live longer. Generalists have to work harder. They are rarely as good as the specialists at any one thing, but they are not too bad at meeting the Big Three. And only Generalists go into space.