6 years? They didn't have access to all that technology when the Stargate program started. They only got bits and pieces over the years. And it's quite a stretch to accept going from contemporary space shuttles to hyperdrive and incredibly advanced technology only a small number of people have been exposed to/have knowledge of for a few years and build a whole starship out of it in just a few years.
The Asgard fabricated the entire engine system for those ships, basically assembling many of the engine systems and having the Humans slowly build the ship around them. Two Daedalus are worked on at a time, with nearly the entire Stargate Program budget spent on them, taking a year to produce the two.
Since the Asgard are gone, there are a limited number of Hyperdrive cores lying around to use, the Daedalus project will come to a halt with a specific number of ships that they'll have to take very good care of.
After that, Humans will have to build a new generation of much less advanced ships entirely from scratch taking years per ship, that will bolster the existing fleet. This is a temporary boom of technological progression with bucket loads of alien help. It won't last.