In that context, Heston as a young hunk was a prop who spoke well. If we ask how come he didn't grow artistically and change with the times, we already know the answer. For one, there are few who can do it. Paul Newman is one, but the list is short. More accurately, it boils down to the range thing.
Audiences can stomach pompous men when they're cute.
It would take him decades to realize this, but it's nonetheless true. Taylor is no Acquarian age hero, he is the last Gary Cooper, the last western hero whom audiences will follow anywhere, even to the Statue of Liberty and the sobering realization that their destruction is inevitable.