I could be misunderstanding, but it looks to me like an Atlas V HLV has about 1/5 the lift capacity of a Saturn V. I know materials are better now, but I'm not convinced they are 500% better. Furthermore, the air, water, food and crew is a fixed mass. I doubt an atlas could take a person to the moon and back even if the structure and fuel are massless.
Oh, i am dumb. yeah, I guess an atlas would be fine. It would take a lot more trips to get the vehicle built but the reuse of existing tech is probably far cheaper that building something new.
