And A320s are flown LAX-CVG so they can easily make it
They have 18 A319NEOs on order, which was 20 originally. And we're talking about SNA-MIA, not LAX-CVG. LAX runways are twice as long as SNA. The A320 CEO or NEO would be heavily weight restricted to fly anything over 3 hours from SNA, IMO.
SNA has the advantage of being a west coast airport and all flights travel east with the prevailing winds. CO used to do SNA-EWR non-stop.
CO sure did operate it with a 73G and UA still operates it with a 73G.
DL operates SNA-ATL with a 757-200.
UA operates SNA-ORD with an a320 and 73G, AA is 738.
SNA-IAH is a mix of 738, 73G and A320.
SNA-DFW is all 738.
It's 3.5 hours SNA-ORD, both DFW and IAH are just a hare under 3 hours and all can be done on just about any 737 or A320 family aircraft without a significant weight restriction.
Atl is 4 hours and DL does it with a 752 so they can take as many people in one trip without a weight restriction, and UA does EWR in 5 hours with a 73G, which they could use a 752 or A319 if they wanted.
Like I said, F9 couldn't do MIA with anything more than an A319.