Fleets built with the Hyperion upgrades, the jamming and accuracy devices, and with more logistics can clean the floor against fleets that don't have it.  

Unfortunately, you tech so fast that it's almost ALWAYS better to wait for the next line of techs before building up your fleets.  

Combine that with the fact that the AI dithers for 20 to 30 turns after declaring war on you means that you have more than enough time to research the necessary techs so that by the time the AI sends it fleets at you THOSE FLEETS ARE ALREADY OBSOLETE.