Without sounding like I want to start an argument, the RF modules inside the vast majority of ISP routers are garbage. Most run at the maximum gain and have poor thermal dissipation. In addition the antenna design is poorly optimised as they go for aesthetics over performance. It’s for these reasons why the coverage and data rates are poor with ISP provided routers.
The chipsets vary as well, some of the better ones provided by ISPs use Broadcom which are based on a licensed ARM architecture, however a number use cheap Chinese designed chips.
Having an ultrafast broadband connection and using a cheap router is like having a Porsche and fitting it with the cheapest tyres you can find, it will work but you won’t get the performance you expect.
