If we assume the card is suboptimal (e.g. because the reach is lower than expected), then the necessary conclusion would be to buy new hardware or alternatively to change the location of your device or use cables instead.
Right now, there is no proof the card is suboptimal, nor for the card working well. To proof the later, you could provide throughput / latency tests (e.g. via Iperf. Check this out) for clients that are right next to your accesspoint. If then connectivity issues still exist, then obviously something is very wrong, but if you get great signal, then is that not proof that the hardware is ok?
If we assume the hardware is ok, but there are some edge cases with regard to latency / throughput / connectivity and reach, then that could potentially be fixed up to a certain degree with different software or different configuration. But only up to a certain degree. There are still hardware limits.
You could try various stuff like enabling / disabling software flow offloading or hardware flow offloading (network > firewall). You also can try to disable/enable packetsteering across all CPUs (network > interfaces > global network options).
You could try to bring down bufferbloat/latency via manipulating AQL queues as suggested here: Belkin RT3200/Linksys E8450 - AQL and WiFi Latency - #42 by patrakov
Roaming / meshing can have negative impact on throughput, latency, but you are not using this, as far as I am aware.