Ok from a pedantic view then I agree, it would be exceedingly hard to rebuild the SaturnV. But that's the wrong question because building a SaturnV is only interesting from a historic perspective. The real question is have we lost the ability to build a high mass launch vehicle and the answer is definitely no.
The SaturnV had a 140,000KG mass to LEO capability. The Block-2 will have a comparable 130,000KG mass to LEO capability. Admittedly there's not one sitting on a launch pad right now but that's because there was never a need for it. Now that there's a perceived need we're building one. It's in the design and testing phase now but that's because they are in fact bloody complicated.
The whole 'we can't build a SaturnV' meme is interesting as a testament to the failings of compartmentalized design and poor record keeping but it's not evidence of some lost technical ability. We're not any dumber now than we were 50 years ago, or smarter for that matter. About all one can say is there's more headwind now from bureaucracy than there was 50 years ago but that's a process problem not a technical problem.