What's the bet you started your portfolio when the ratio was 4.1.Lets have a look at what you suggest, houses at 4.1 median income ratio.
A cheap section, small 200sqm ish in South or West Auckland is $500k, if you can find one.
A 100sqm two story house is $3000 per sqm.
Ancillary work, driveways, fencing etc, $30k
That is $830k, without leaving any profit for the developer and nobody does this for nothing.
Median income, say $70k pa.
On your proposal, that house should be $280k. Who pays the other $550k of actual costs?