Oh, come on. George Reeves played Clark and Superman exactly the same. And he didn't even have the opportunity
to demonstrate the kind of physical performance in flight that Reeve did, because he wasn't on wires. It's a ludicrous comparison.
And I completely disagree that Superman should be built like a bodybuilder. For one thing, muscle bulk is not an indicator of strength. Bodybuilders enlarge their muscles for show, nothing more. Real, working strength doesn't require bulk; the physically strongest people are generally lean and wiry, not bulging.
For another thing, when would Superman even get the opportunity to exert himself enough to build up really big muscles? For him, lifting a car is as easy as lifting a pencil for me. He wouldn't need to be excessively muscular to do his job.