"There are fifty who can reason synthetically for one who can reason analytically."
This certainly means that "Out of 51 people, only one can reason analytically."
The whole quotation states:
In solving a problem of this sort, the grand thing is to be able to reason backwards. That is a very useful accomplishment, and a very easy one, but people do not practise it much. In the every-day affairs of life it is more useful to reason forwards, and so the other comes to be neglected.
with the final statement:
There are fifty who can reason synthetically for one who can reason analytically.
This appears (by reason of the quoted ratio and the language of the first sentence) to equate "reason synthetically" with "reason forwards" and to equate "reason analytically" with "reason backwards".
Therefore, in that the statement says:
... the grand thing is to be able to reason backwards. That is a very useful accomplishment ... [that] comes to be neglected.
I would agree that it implies that
A person who reasons analytically is a ... valuable asset
Whether it also implies that
.A person who reasons analytically is a more valuable asset than 50 persons who reason synthetically.
is not entirely clear, but does not seem (to me) to be an unreasonable interpretation of the quotation.