Gateway groups weight number
is there a reason why gateway groups weight number can only be 1-5 not giving more granular control like 1-10 could give ?
I don't believe there is any underlying limitation there. I think that someone in the forum asked if the range could be made 1 to 20.
A wider range can be handy if you have gateways to balance that have very different bandwidths - e.g. a 10Mbps and 1Mbps link. The "trouble" with such widely differing speeds is "after-hours" when the number of users is low. Every so often a state gets allocated to the 1Mbps link, and the client program associated with that state only gets 1Mbps download speed, when actually the 10Mbps link is likely under-utilized by 10 other states that are not doing much (or finished long ago…).
Anyway, that is for the sys admin to decide when setting up these things - allowing a wider range of weights would give the flexibility.
IIRC at least at the time, there was/is a limit to the length of the list of addresses for route-to in pf, and the weight limit of 5 was chosen to keep things short enough. Since it's not a true weight and just the gateway IP address repeated X times, allowing more entries makes the lines much longer.
Imagine someone with 5 gateways in a group for LB, each with a weight of 5, so that's 25 IP addresses printed out. Now imagine that with an upper bound of 20. Sure, that's not exactly what someone would typically do, but even worse case "correct" scenario is X gateways at max weight and 1 gateway with a weight of 1.