Pretty much. A frontal assault on Earth would only end up in one of two ways:Not necessarily. Their fleet is pretty large. If they were desperate they could muster the entire thing.
Earth has superior technology and potential allies who could help if it became necessary. The Lucian Alliance would still be slaughtered. The Lucian Alliance attack on Earth is a stupid storyline which would be best left forgotten. There are other things the show could be focusing its time on.
a) Antarctica Base turns the ships into burning hulks in orbit
b) The upgraded battlecruisers play a fun round of "slice&dice 'em".
Over the years the writers have written themselves into a corner by adding a new deus ex machina every other week.
The drone chair was destroyed in the Atlantis finale.