[stomachmonkey]

Is your main router dual band?

Signal strength does not always equate 1:1 with performance.

There are two frequencies, 2.5 and 5.

2.5 is for distance and slower

5 for speed but has a shorter range.

Also, wifi extenders do not give you full throughput of the primary router.

Think of the signals like circles.

Closest to the device is 100% and at the edge of coverage is 0%.

If the devices circles overlap in the middle the extender is only repeating 50% of the signal.

Then there is backhual and a host of other things like WIFI penetrates OK in a horizontal but sucks at vertical.

WIFI is meant for convenience, not performance.