One simple way of verifying the latter case is by looking at the number of senses assigned to the prepositions by a resource  Table 5: Confusion matrix for L1 data -prepositions such as the Oxford English Dictionary.
we find no good correlation between the two as the preposition with the most senses is of (16), and that with the fewest is from (1), thus negating the idea that fewer senses make a preposition easier to learn.