Probably true. However, the 'rating' of a switch usually relates to the maximum current it might be called upon to break, so I'd be perfectly happy to have lights supplied by a '6A' switch (and 'protected' by a 13A fuse). Under what circumstances could the switch be called upon to break more than 6A?I think 20A switches are more expensive than an FCU though.
In the case of a fault downstream of the switch, a fault current of probably several hundred amps would flow (until some OPD operated) - but if a current of 'several hundred amps' is flowing through the switch for a very brief period of time, it hardly matters whether it is 'rated' at 6A or 20A!
Kind Regards, John