Maybe I should ask your position?
Farmer, technician, assembler, designer, parts support, tech support, sales, warranty, therapist, etc.  What ever the role is, I use my knowledge to help those around me.  Perhaps I may hold back on helping the competition, but 

Maybe you just came from working with horse pulling growers or 4020 with synchro transmissions and chsin driven equipment, I don't know.  And there is nothing wrong with that. In that case a grower looking to step up would find your level of knowledge helpful. I am referring to guys with at least powershift technology if not ivt and have fairly modern fully equipped jd and or PP type equipment.
The tractor in front of the implement is merely powerplant to move and operate the implement.  It does not matter if the controller is installed on a 4020 or an 8400R, it is the controller and implement that will determine the accuracy and the precision since the tractor is merely a powerplant.  All the tractor features you mentioned merely make it more convenient for the operator, but do not affect the performance of the attached equipment.  Like your 350 excavator, you can install larger pumps, turn up motors, and add technology to older equipment and get it to outperform a new machine but it still takes time and money.  IVT, ILS, PS don't make the planter plant better and sometimes they make performance worse.  VRTing with a 4020, 2630, 6000 globe, ATU200, and ISOBUS rate controller works just a well as on a 8400R after everything is calibrated.

I will admit that I don't write the Rx because to me the hardest part about VRT is getting the right info on the Rx map and is best left to the agronomist; getting the machine to apply the product/seed accurately is a walk in the park.

Knowing the limits of the technology is key, not just what the factory default settings are.
The key is understanding the machine's limits and how to apply technology to optimize the performance of the machine.  Knowing you can tweak valve and meter cals to increase response rate is great, so is adjusting look ahead and .  Having a machine respond like an old grandpa driving with 20% throttle, 20% brake, and 500ft lane visibility is less than desirable, but neither is making if function like a teenage driver that uses 120% throttle, 120% brake, and 100ft look ahead.  Typical a 

I'm no technician of that kind of hardware. I'm an operator doing work for other operators.
I guess you are the VRT god since you have been VRTing for less time than the JDRC2000s and 2020 Gen2s has been out, let alone its predecessors.  The trouble is I remember VRTing with the JDDRC, the predecessor to the RC2000, and prior to that using Viper Pros, Viper 4s, Vipers, and even the old SCS660 and using 2020 Gen1s.  But I guess since it only takes 7 years to become an expert you should know everything there is to know about VRT.

FWIW 95% of the Deere techs I have talked to don't have a clue how rate controllers work so it comes as no surprise that they would be of little help to you in the past; now get on the phone with an AgChem and you can learn a lot and have a whole different experience.  There is a reason AGCO did not let every dealer sell AgChem and it had a lot to do with customer support and trained the customers how to optimize their equipment which not every dealer was capable of.

IMHO, there is nothing wrong with tweaking things to improve performance since everyone's operating conditions are different and no machine is ideally tuned from the factory although most will work adequately from the factory; the top level precision requires adjusting the machine for your conditions.  At some point you can only tweak so much because trying to make a Ford Ranger pull like a 359 Pete is just reaching for the stars.  For some guys nothing factory is good enough and some of them would go so far as to scrap the design for an anvil just because they broke it.  A lot of guys try to shovel 10# of crap in a 5# sack, and for the ones that are successful they were still shoveling crap.

I'll call you next time I need your level of help.....don't hold your breath.
If you do happen to call I will gladly help you figure out your issue.  Luckily for me the fundamentals of machine operation have not changed, only the hardware has and the machine is not the one writing the Rx.