Humane, if you've found the AI to be weak at invading you then you must be playing at a fairly low AI intelligence level. At the higher levels they have no problem at all systematically killing all your defending ships and then sending endless transports until your entire empire has been smashed into little mewling pieces. Not that I've ever had that happen to -me-, of course... *whistles innocently*
I very much like the split between assault and invasion craft in GalCiv, I don't want another Moo2 where you make a fleet and run around sterilizing everything. I'd hate to see the +soldier techs in GalCiv become as useless as they were in Moo2. With the dual-assault needed to take a planet in GalCiv a civlization can still be amazing hard to conquer even if you've knocked out their navy if they have a better ground tech than you. Expensive too, in terms of the population you lose in the attempts.
I've had my ground troops resist invasions long enough for me to turn the tide of a war, if the ships that first showed up could have bombarded too then I'd have had no chance to do that.