Why a giant jet flying boat still looked plausible after 1945

How unreasonable was the proposed Saro Queen jet flying boat?

It was technically and operationally plausible for a short post-war window, but improving land-airfield infrastructure steadily reduced its advantage.

The proposed Saro Queen was a jet-powered development of the large Princess flying boat. In the late 1940s and early 1950s, stretches of usable water still greatly outnumbered runways capable of handling very large aircraft. That made a high-capacity flying boat potentially useful for crises such as the Berlin Airlift, where access was the central constraint. The concept nevertheless faced a narrowing opportunity as land airfields became more numerous and better equipped.