I’m not from Missouri but show me anyway...
The perfect ET (we are in fact observing an alien invasion) would be ET’s beating sword into plowshares, enslaving the world to manually farm, and mine. Taking earths natural resources back to its home world, including water and air. The population would die off eventually but not before extensive species research through the employment of anal probes and spinal taps...
There, I think I covered most dystopic ET Invasion scripts written.
A very advanced alien species would be building their own stars snd solar systems. For them, only one thing here would have value. And of course the average hairless ape sees no value in that thing.