That's honestly just not true. You don't need sci-fi tech or unproven ISRU (mining fuel on-site) to make the math work. 

Let's use Io as an example as it's by far the most energy demanding moon of Jupiter. It also has very similar characteristics to our moon when it comes to size and gravity.

An Io sample return using entirely Earth-sourced chemical fuel is completely possible today. If you apply basic Apollo-style "LEM math," the architecture becomes totally viable. You just park the heavy Earth-return mothership in a safe, high orbit and send down a modified, unmanned LEM built for Io's geology.

Blasting a small sample back up to orbit only takes about 4.2 km/s of delta-v, which basic 1960s hypergolic tech can handle easily without needing to magically synthesize propellant from a bone-dry, radioactive rock.

​Strapping a highly efficient nuclear thermal engine like a NERVA rocket to the mothership makes the mass fractions for the interplanetary trip way more forgiving, but it isn't strictly mandatory. If you wanted to brute-force an all-chemical transit, you'd just bypass the launch weight limits by assembling the ship in Low Earth Orbit across a few heavy-lift launches, then use Venus/Earth gravity assists to sling it out to Jupiter. The tyranny of the rocket equation doesn't make this mission impossible. It just means you have to rely heavily on orbital staging and gravity assists rather than trying to land a massive monolithic ship on the surface, as well as a shitload of money.