I suspect that one of the reasons the SA 8 speed works well with small wheels is that they allow use of a sprocket input ratio that lowers the torque input level to the hub. With a normal 26" or 700C wheel the input ratio that would be used by many, large input sprocket and small chainring, subjects the hub to very high input torque levels.

Prior to the takeover of SA by Sunrace all SA gear hubs whose manuals I have downloaded listed a minimum input ratio of 2 to 1, that is the chainwheel with twice the teeth of the input sprocket. With standard size wheels, if followed with the SA 8 speed, this would give a low gear of 50+ gear inches and a high of 150+ gear inches, not satisfactory for normal uses.

Typical gearing on old 3 speed Raleighs was closer to 3 to 1, lowering input torque substantially. This, in part, might be one reason for the SA 3 speed hubs reputation for excellent reliability. Rohloff, SRAM and NuVinci still list minimum input ratios for their hubs. Rohloff is adamant about their recommendations, I presume due to it being marketed to strong athletic riders for MTB use as well as tandem riders. Most other gear hubs marketing seems aimed at casual and urban riders and bikes generally speaking.

Both my Swobo Dixon and Civia Hyland Rohloff came with the factories with gear ratios substantially above manufacturer listed minimums for the hubs. The iM9 has a factory suggested minimum input ratio of 1.73 to 1 while it is delivered with 19/38 gearing, giving a 2 to 1 ratio. The Rohloff has a minimum input ratio listed as 2.35 to 1 and the Civia comes with 16/45 gearing, giving a 2.81 to 1 input ratio. I thus expect both hubs to last a long time. In building my gear hub bikes I also follow recommended input ratio minimums when available.