If corvettes can effectively take on a ranger, then check to see what military resources they own. Find each of those starbases with the red cones on the map, and kill them. Or have someone else kill them. But the point is to destroy those bases!
The middle range of the tech tree already has an immense attacker's advantage. The defense ratings of everything from battle cruisers to dreads lack behind the attack rating (battlehammers are a special case). So, the guy who fires first has a definite advantage already, especially if you happen to see his stats and they say attack +150%! But, until you can take away that resource advantage and make it your own, go on the offensive. Attack, attack, attack! Then fade away, to strike again another time. Be the guy who shoots first.
Granted, there are cases where you will have to be on the defense because you get jumped or are overextended after attacking, but have good recon abilities and generally be on the offensive. Think like a fighter pilot. Defense is only useful in a dogfight if you use it to either gain the advantage to kill the other guy or use it to get away.