Well that's why I suggested remove the rare metal cost. By removing it you can build early on Laser/Microwave, EMP, Stickyform or Railgun/RPG Panthers without the need of a rare ore smelter. Mid-game this would be a very powerful and nasty combo, when you don't have a rare-ore smelter up, or a rare-metal mine, and save the metal for building GPs and such.
As you recall a tiger does use rare metal and usually a lot of it. Until you had a steady supply of rare metal a tiger is not practical. So early-mid game the panther becomes quite useful with its higher HP, and better armor. Could use it for a great base defender at that point... maybe not the greatest for assaulting a base but ya.