Originally Posted by
Vcize
Upgrading to Comfort Plus when booking through Delta was showing an extra $100 per passenger. On AmexTravel the Premium Economy was an extra $2,000 per passenger

Comfort Plus and Premium Economy are 2 different products and Amex is offering both in the booking flow, albeit neither one is only $100 extra per passenger. In that case, I would book Main cabin via Amex and then upgrade to C+ via Delta for the $100 they want.