I agree - once one gets above 25 clients per AP, one becomes limited on the 802.11 channel overall…
Standard rule of thumb for sizing/capacity is 25 client stations per AP depending on the traffic mix
Much depends on the traffic - IOT apps, could be a lot - VOIP/Media Streaming/Gaming, much lower.
As noted - B1300/S1300 are pretty stout on the GL-iNet builds based on the QSDK, they’re optimized fairly well by Qualcomm/Atheros here.