Finally, I upgraded again to Ubiquiti UniFi (UAP-AC-LR and UAP-AC-Pro) a few years back. I've never had a problem since. Even when I ventured into smart home devices and IoT earlier this year, which pushed our WiFi count in excess of 60 devices, the Ubiquitis didn't even break a sweat.
This screenshot I took just a few moments ago.
Now that we're on PLDT Fibr, it makes more sense to have a stable WiFi connection all around the house. I never liked the idea of WiFi repeaters or even powerline adapters. My philosophy now is that, if WiFi coverage is required in a certain area, it has to have an AP wired to it.
Anyway, I'm so satisfied with Ubiquiti that I'll probably run these to the ground before I replace them. And if you think they're expensive, they're actually not. If you buy them from Amazon and have somebody brought them here (if you don't have a courier), they're probably even cheaper than those "boutique" wireless routers from Asus, Netgear, Linksys, or D-Link.