The USN got decades of experience with the catobar carriers, if the CVN-78 is working fine in all systems, then it should become combat ready in a very short time.
China needs several years because it was our first time to operate a carrier, while the CVN-78 in its way of operating is not a radical change from its predecessors.
That's probably extremely understate the Weapon testing procedure the US have, you probably don't know how US test their weapon.
Weapon testing is not like what you said : "since we have experience operating something, something, we should have no problem working out new weapon system that similar to the one we used before."
Let say, for example, M4 Carbine. How long does it take for a XM4 to be accepted into service? While the US Army have been using M16 series weapon for the last 20 years?
It took 8 years for XM4 to become M4, XM4 was designed in the 1984 and ended their prototype phase as a end product XM4 in 1991. Accepted into Military service in 1994 but not after 1999 before major unit started fielding it. And in 2003, Major unit (such as 3rd Infantry Division) is still using old M16 to fight the war in Iraq.
The problem is, even M4 share 85% of M16 parts, 3 things were different between M16 and M4 that warrant such a long testing time. Shorter Barrel from 20 inch (M16A2) to 14.5 inch (M4) which mean the ballistic is different, which translate to stopping power, accuracy, the use of differnet munition would have different outcome. It take the Army 2 years to be able to make a blank firing adaptor that you can use in M4 because taking one out from M16 and use it on M4 would destroy the barrel and the bolt, because it was designed to use by a 20 inch barrel, where the recoil did not dissipate that well when you use it on a 14.5 inch barrel weapon.
Another major change being M4 is a modular weapon versus M16 fixed design, you can take out the carry handle, change the telescopic stock just adding a M203 by screwing 2 cap screw under the fishbone of a M4, instead of have to take out the hand guard and replace it with a M203 unit. Doing so would mean weight distribution of the rifle would be different, adding an ACOG on top of the bridge would experience difference when you fire than without an ACOG, because the weight of the ACOG is added. Using ACOG and Using some other scope/optic would also have different result, because the weight is different, using a M203 attachment and fore grip would change the accuracy because the weight ballast on the front of the carbine (M203 is a lot heavier than foregrip) which mean you will need to adapt to a different firing position when you are using different attachment.
The last thing M4 changes form M16 is the round, which is more heavy because it wanted to retain the 1 in 7 groove M16 have, heavier (or magnum round) would result to different soldier fighting habit, how they perform the weapon cleaning, how they manage their fire (which we were told not to use 3 round bursts in M4 as often as you would in M16)
Even tho only 3 changes, and 85% the same parts (Not similar, the same, you can pluck it out of a M4 and put 85% of your parts into a M16 and vice versa) It basically took 9 years for soldier to train how to fight with an M4. I don't think M4 is a failed weapon because it take that long time for training/assessment, even tho the US ARmy have been using M16 and XM-177 since 1960s.
In this case, a ship is a lot different than a rifle, at least I don't live with my rifle (I fight about 4 to 6 hours a days in my rifle, the other time either is behind my shoulder or unloaded in my barrack, but if I was serve on an Aircraft Carrier, I will need to live in my ship, which only mean they would have a lot more issue, technical or practical that they need to solve before making the ship design official. I don't see how because the US has Nimitz class, which mean the Ford Class would have been smooth sailing because there are not much of a change.