First of all, Falcon 9 is a heavy lift vehicle. Falcon Heavy is a super heavy lift vehicle. Exactly the same class as SLS. The biggest issue is that SLS is not

First of all, Falcon 9 is a heavy lift vehicle. Falcon Heavy is a super heavy lift vehicle. Exactly the same class as SLS. The biggest issue is that SLS is not even available. NASA flagship Europa Clipper mission had to be moved out of SLS to Falcon Heavy due to lack of availability of SLS. Also interplanetary travel is not only in scope of nation states, but also private companies. Perseverance rover has been launched on ULA Atlas V rocket. But more importantly SLS+Orion can not deliver people to the surface of the Moon. That's the job that NASA has given to Starship and SpaceX. Also, huge chunks of Lunar Gateway (let's skip the fact that Lunar Gateway is useless in itself) will be delivered by SpaceX with Falcon Heavy. Also, resupply of Lunar Gateway will be done by SpaceX with Dragon XL. Without SpaceX Artemis program will be failure whether you have SLS or not. But you could get rid of SLS and Orion. You could use Falcon 9 with Crew Dragon or Boeing Starliner to load people to Starship in Earth orbit. Then you could send Starship to the Moon. It goes there currently anyway. The kicker is that Starship will have the same internal volume as ISS, many times bigger than Lunar Gateway + Orion.