I don't think this year has true franchise QB. Ward IMO has the best chance to turn into one and Sanders could end up developing into a top ten to top 15 guy just outside of the franchise level. (Much like Carr) Outside of those two, there are boom or bust types that seem more likely to bust like Millroe and Dart. IMO, you should always be taking lottery tickets on QBs in the draft because you never know when you get lucky and hit on one.
Also, you never know when a guy is going to take a big leap in one year in college and turn into an elite prospect so there could be one in the draft next year even though I think Manning does not enter the draft until he graduates. Guys like Burrow, Daniels, and Nix sometimes develop in their last year to become elite prospect in the draft out of nowhere. So, you never know which year that happens. It didn't appear to happen this year but it could happen next year with Nuss, Jr., Drew Allar, or any number of other guys we aren't even thinking about right now.
Anyway, the Saints should not let keeping Carr this year stop them from drafting a QB in the draft this year if they see one they like and they are in position to draft him with good value.