That's a fair answer and if I was a Giant fan, I'd have some serious consternation as to which way to go here as you seem to be having.
I think it all comes down to this, and you mentioned it...will Darnold be alot better than Jones will be or will the gap be negligable...that's it in a nutshell...yes?
Barkley is no question a transcendental talent and like you say, he has the tools to end up being the best RB of the last 10-20 years. However is Darnold going to end up being an all-pro caliber type player for the next 10 years? Will he lead the Jets to a Super Bowl? Is Daniel Jones going to end up being more Dave Brown or Eli? That's what it's all going to come down too.
This may be a cop out but when I look into my "crystal ball", I have a feeling when it's all said and done, both franchises are going to feel as if they made the right call and it will end up being a win/win for both. My opinion is Darnold will end up being a Top 10 QB within the next 2 years and has upside for Top 5 QB stats once the Jets fix their O-line and bring in a few more top notch skill position players on the outside which might not happen for a few more seasons.
On the other hand tho I don't see Jones coming close to being an all-pro or close to be a Top 10 type guy I do see him being no questions startable...a Kirk Cousins type of QB which is fine and most Giant fans will be ultimately be happy.
This going to be fascinating and alot of fun going forward for all Jet and Giant fans as we get to see and compare how both the 2018 and '19 drafts ultimately work themselves out and where both our teams end up doing.