How the Big Five (Big 5) normative personality test revealed as .... incomplete

Short answer: thanks to commingling analysis.
Commingling analysis is a statistical method for distinguishing between one (usually normal) distribution and a mixture of two or more distributions.

The HEXACO model is replacing the Big Five normative personality test now!

Online dating sites using the Big Five model could be considered obsolete sites, because the Big Five model has been proven as "an incomplete model"
As some of the subdomains of the main domains of the HEXACO model are different from the subdomains of the main domains of the Big Five model, it can not be simple added the scale of the Honesty-Humility factor to the Big Five model to upgrade the personality test to the HEXACO model.  I think, legally, online dating sites using the Big Five model of personality could be considered a FRAUD because they are using an incomplete model of personality. They are assessing 5 scales and not 6 scales.

Online Dating sites have very big databases, in the range of 20,000,000 (twenty million) profiles, so the BIG5 model or the HEXACO model are not enough for predictive purposes. That is why I suggest the 16PF5 test instead.

Also some Psychologists began to encourage the use of other tests for the Online Dating Industry, like:
California Psychological Inventory (CPI)
and
The Millon Index of Personality Styles-Revised (MIPS Revised)

but my best recommendation is, of course, the 16PF5 normative personality test.
Nor the CPI nor the MIPS can outperform the 16PF5.