doublebogey7
Head Pro
As there is with many of the rules, hence the need for clarifications.I think what you say is largely irrefutable common sense. But I think it is also common sense that this text from the relevant clarification (or something very much like it) would better belong in the players' book.
It would not take up much page space.
"... it may be possible for the player to measure the two club-lengths from the reference point across the penalty area in determining the size of the relief area."
Generally, I think that most, or a large number, would assume there is no more to the rule than what they see in the players' book and not give any consideration at all to the clarifications.