If both projects had gone head on their initial timescales, it could be argued that the USMC might have been so impressed with an F35 on a ramp, as I recall they liked Harriers on ramps off the Illustrious class, that they might have ordered a number of QECs.
Highly doubt it. The US Navy specifics the "carriers" they want, and something as big as the QEC would be counter to the current LHA/LHD classes and the super carriers, and in betweener if you will. Yes, US Marine Harrier pilots were impressed with the ski jump when they used it, and outfitting ski ramps to the LHA's/LHD's over the past decades has come up periodically but this was dismissed with the thought that ramp taking up to many helo spots on the LHA/LHD, and the flat deck was deemed to work well enough for the Harriers.
Conspiracy theorists would also opine that the carrier admirals would see a large deck STOVL carrier as a direct threat to carrier orders, and worry that politicians may decide, "hey lets buy cheaper carriers" and risk future conventional carrier operations. As most would agree, cats and traps allows for greater payload off the deck and for aircraft that are not as compromised with STOVL penalties.
Thirdly the US has a robust ship building industry, with very strong ties to US congress. Why buy from a foreign yard? Legal obstacles as well.
Fourthly, the QEC is partially designed to commercial standards. US warships are designed to military specs. Likely a non-starter.
The LHA/LHD and carrier mix seems to work well with current US doctrine. The LHA/LHD is designed to support robust amphibious ops, helo ops and imbedded Harriers and soon F-35's to support the task group. The aviation heavy USS America gave up other capabilities to support more aircraft, but looks like that will not be repeated for future orders.