It is. That's why much of the WGS action these days is not is sequencing individuals in the clinic, but rather in large-scale population studies like UK Biobank. These are aimed at identifying interesting genotype-phenotype relationships, for which you need massive sample sizes. This approach probably will bear fruit eventually, but the outcome won't necessarily be that everyone gets their whole genome sequenced; rather, the discoveries will be translated into the clinic via either (1) targeted tests that assay specific variants discovered via the population-level studies, or (2) drugs developed on the basis of gene-disease associations.

This chicken-and-egg problem is also the reason why Illumina has invested massive amounts of money in companies like Helix and Grail, which are basically highly speculative attempts to find a problem for which loads of Illumina sequencing is the solution.