Why the 170-gun HMS Duke of Kent stayed on paper

How powerful a symbol would HMS Duke of Kent have been, and why was the 170-gun first rate never built?

It would have been a major prestige symbol, but British dominance made that expensive statement unnecessary.

The proposed 170-gun four-decker would have been a conspicuous symbol of British naval power. Such an expensive statement made little sense while Britain already possessed overwhelming naval prestige. Rivals were not threatening that position with ships that required a still larger British answer. In this interpretation, Duke of Kent stayed on paper because the Royal Navy did not need to pay for that additional display.