@Amplitude 

Hi,

Leaving the cheapest of Wi-Fi routers aside, the limiting factor for a Wi-Fi router's signal power is mostly not the technology used. 

The limitations are mainly the various regulations for RF equipment that governments around the world have come up with.

For example, in the European Union the maximum power level (EIRP) in the 2.4 GHz band is limited to "< 100 mW".

So how does that work?

In the factories where Wi-Fi routers are manufactured there are calibration stations (basically shielded boxes with an antenna inside and some RF measurement equipment connected to it) located towards the end of the production line.

Within these shielded boxes each assembled router, no matter if it's an Archer AX73 or a Vodafone Station, will be calibrated to output a signal with an EIRP of maybe around 95 mW (for 2.4 GHz, European Union). The manufacturer needs to leave a bit of margin in order to avoid the risk of shipping out non-conforming devices.

Of course, better antennas or antenna arrangement should improve the router's capability to receive the Wi-Fi signal sent out by client devices. (smartphone, etc.)

What that means in practice is hard to tell, though.
Network communication it always two-way. So, even if a Wi-Fi router with larger external antennas could still receive a weaker signal from some smartphone than a router with small internal antennas, if conversely the smartphone can't receive the signal from the Wi-Fi router, then there still won't be any networking possible.

All the adjustment of RF performance you can (legally) do on the Archer AX73 is to set “Transmit Power” to “High”, but “High” in this case means the legal limit, as described above.