I beg to differ, and adding Primitive BattleMechs is completely logical from the standpoint that we know, in many cases, the designs of 3025 were an evolution of previous designs: just look at the original fluff text for 'Mechs like the Shadow Hawk or Wasp, which make it clear they evolved into those forms. Codifying the rules that made these earlier 'Mechs makes sense to me.
Of course, you don't have to like it, but if your primary complaint about a Primitive BattleMech is that it's a Primitive BattleMech, my advise would be to move on.