Not all 5Ghz channels are affected by the DFS requirement. The DFS channels are more country specific than other WiFi band frequency restrictions. Usually the best course of action (or at least the one my coworkers and myself take) is to simply deny the band plan the use of those channels.

A lot of consumer routers I've seen don't even expose the DFS channels as an option to avoid this problem (looking at you Motorola mesh products). It's not a problem just kind of funny to see.

Put simply there will be two aspects taken into account in the 5GHz Wi-Fi design.

Firstly, a coverage aspect of the design which will ensure that any given spot has a primary and secondary (and sometimes tertiary) AP radio providing appropriate RSSI.

Secondly, a channel plan that ensures that the DFS channels are not allocated to the primary and secondary radios. So if a client station's primary AP get taken offline for a minute by DFS then that station can immediately roam to the stable channel and maintain a decent RSSI.

Additionally, there may be some environments where the DFS channels are not enabled on the equipment at all. For example, many cheaper devices (think low end android phones) don't support DFS channels at all, so if there are many such devices in the area (e.g. College campus populated by poor students) then every radio running a DFS channel is effectively a coverage hole and therefore better to not use those channels at all.

obtaining the govt certifications for using DFS channels does add to the cost of the chipset so cheapest chipset simply don't do it.