Then fire the cruft staff of the FAA and buy more test equipment and pilots or analysts. That's a terrible excuse. The FAA has been certifying craft for 60 years now. Much of this is highly understood and predictable. If you can have 6 craft in the air 7 days a week for a year and not have certification complete under smooth circumstances, the certification process is bloated in ways which would probably infuriate even the most cautious tax payer.
I'm afraid you have little idea of Federal Aviation Regulations (FAR's) and the testing required to satisfy them.
Let's correct one thing. The FAA/EASA do very little actual flying. Most testing is done by OEM pilots who are delegated by the Cert Agencies. In fact Cert Agency personnel will not set foot an airplane until enough testing has been done to show that it is safe and reliable.
And very little tax money is expended, test costs are borne by the OEM's.
Read through AC25-7D. It outlines the certification flight testing required to satisfy FAR Part 25. Then try to devise a test program that can demonstrate all conditions in a couple of months. Don't forget the remote testing to find icing conditions or limit cross winds. Iceland is a good bet for both but only if it's the correct time of year.
Then you'll also need to do the Community Noise testing (Part 36), ETOPS demos, Frequency and Reliability at airports around the world... The List goes on and on.
In addition, a large portion of the testing does not involve cert work. Fuel mileage is not required for Part 25 Cert. It is very important for success in the market place though. A significant portion of flight test is dedicated to proving that the airframe/engine are meeting their cruise performance drag and SFC design criteria.
And of course sales demos and trips to the Paris/London/Dubai air shows that have to be built into the schedule.
Plus there are always a few surprises, like the 777-9 cargo door, that crop up and may require re-test.
The OEM's have been developing, certifying and delivering commercial airplanes for 60 years. Testing costs time and money, they run very lean test operations to minimize the effort. The typical 12 - 18 month test programs don't have slack time and no repeat testing that isn't required to correct a problem.
As a final note, the 787 Program planned to have a 6 month test program. It didn't turn out well.
Please do a little research before making grand pronouncements. Knowledge gained in one field may not be transferable to another.