It may be “the standard” but the critical issue is whether or not it does the job and in your case it clearly doesn’t, at least, not to your satisfaction.
There are so many other issues in the noise insulation and so many variables, such as the thickness of the slab and the density of the concrete pour, that using the thickness of the insulation and carpet as the only metric is frankly ridiculous.
The main issue is noise transmission allied to your legal right to the peaceful enjoyment of your lot. If the former compromises the latter, minimum building standards are almost irrelevant.