Let's just be honest here people... If the x-men and the avengers could take on the Shiar's best warrior's(the imperial guard) without breaking much of a sweat, then what hope do the Shiar have against all of earth's heroes/inabitants?
I mean come on now... gladiator consistantly gets whooped by hulk and thor, and he's their most powerful guy. Come to think of it, the only crowning achievement that the Shiar have been able to do is give the X-men the technology to build the Quinjet and Danger Room... ..that's just about it...and to be honest with you... I think Reed Richards could of done a better job...
Now if you compare the accomplishment's of earth 616 technology to that of the Shiar, we're waaay more advanced(ie Creation of sentinels capable of killing powerful mutants who consistantly hand the Shiar Imperial guard their asses, time machines created by Doom and Richards..Creation of adamantium..a substance harder than any substance in the known universe..)
The only way the Shiar have a chance in hell against Earth is if the start f****n with earth's sun like they did(on accident) during operation Galactic Storm. That's not going to happen, because like operation G-Storm, Earth's heroes will be on them quicker than flies on cow sh**.
I like the Shiar people but come on... If they can't win against the Kree or Skrulls(who consistantly get their asses handed to them by the Avengers and Fantastic Four)... much easier foes... they ain't going to be able to touch the people of earth. Nuff Said!!