Mesh network versus a simple Wi-Fi extender

If the network is rock solid, the SQ probably will be fine. If not that is the first thing to improve.

Try cheaters.

I suggest that mesh is the best if you have low interference; things like Microwaves (kitchen) and other devices generate noise and can attribute slow to no network information. Modern equipment falls back to the lowest speed to compensate and, if left to auto for channel selections, will adopt less congested channels.

As for SQ, a packet that arrived is a perfect packet unless it’s not, then it’s sent again till it does arrive perfect, or you get dropouts after X number of retries. It makes no difference in what equipment you choose to use; SQ is the same. As long as the packet arrives...

I use Ethernet Over Powerline boxes so I avoid wireless altogether without needing to run cables. One wireless box is downstairs next to my router and the other is upstairs in my bedroom. It's the best of both worlds and more boxes can be added throughout the house at key places. 

Netgear Orbi WiFi 6 devices are extremely stable. We use a four satellite mesh network in a 5,000 sq ft 1867 brick home that serves as our local historical society HQ and that mesh system was a game changer. Device allocation can be monitored from the phones of our staff, including a hifi Bluetooth streamer in the ball room, where most of our events and zoom meetings are held. Best $2,200 we’ve spent in recent years.