Sure a mild upgrade and spiral update other systems in over time makes some sense. Problem is we know what the USN want and it is more than you are suggesting;
While the Air Force’s NGAD fighter initiative currently paused, the Navy is pushing ahead with its similar F/A-XX stealth jet program. With the Air Force’s NGAD currently paused, the Navy is pushing ahead with its F/A-XX carrier stealth fighter.
www.twz.com
Question is of those requirements what changes from the current generation?
Advanced sensors - You could argue APG-85 is probably as good a current system as can be bought today but will that be sufficient for a new build airframe in 2035... What else will be required from sensors, perhaps LIDAR, next gen EOTS and EODAS for certain.
Advanced Lethality - Is a AIM-260 and hypersonic ASM sufficient for increased lethality? Do we finally see some sort of Directed Energy Weapon especially if we have a twin engined behemoth with plenty of power generation available? It feels like 5th gen platforms are only finally now close to getting 5th gen weapons. How long would a notional 6th gen platform have to wait for weapons to match its capabilities?
Advanced Range - I expect an Adaptive cycle engine brings this. Simply building a bigger aircraft that holds more fuel but with current generation engines probably won't deliver the range increase the USN want or need.
Manned and Unmanned Teaming - No doubt that will be in place for the platform whether a minor upgrade or a full blown platform but where is the CCA that takes off and lands on a carrier going to come from? MQ-25 isn't sufficient nor capable enough for what the USN will need.
How about the EW mission. Will the F/A-XX incorporate the NGJ internally or will the USN push that mission to an unmanned platform.
Will F/A-XX be single or two seat or both?
USN likely have a good set of requirements, have three keen vendors and a slew of good technologies that are reasonably mature but their budget is the least certain aspect. Will the USN have the money to build what they want or will they have to compromise?