My EX7300 has great speed but poor range

I've used one of these and it worked great while using. There's some optimizing you can do that I'll link to.

1. Hvac and concrete do great at blocking signal. have you tried moving it to a different outlet or even a different room. Sometimes a small location change removes an obstacle that was slowing it down.

2. change channels. Sometimes certain wifi channels have interference on them and a simple change of channel improves signal.

3. Distance. Extenders need to be a certain distance from the main router. To close and the main router creates interference. To far and the signal isn't strong enough to extend. Play with your distance.

4. Test. Make sure you're speed testing whenever you change locations. Speedtest more than once in a location. A single bad test doesn't mean its a bad spot, it might just be the device/provider causing issues. Test a couple times and then move it somewhere else and retest.

It takes a bit of playing with an extender to really optimize it for your house. Everyone's house is different so move it around a little and see what it can do. 

https://www.tomsguide.com/us/wifi-extender-setup-guide,review-4133.html