Tablets only as good as your wi-fi connection?

perhaps a faulty model - I have loads of tablets with friends and family all working well

the reason often for issues is a poor wireless signal and interference - so the reason for the xirrus on a laptop was to diagnose possible interference and also have reference data for the signal strength.

yes, but it will also be very dependant on the quality of the wireless signal when you move around - often come across this issue where the signal is not adequate all over the house and so a survey on a wireless laptop with xirrus often reveals the issues.
and then corrective action can be taken to try and achieve a better coverage, sometime involving repeaters

unfortunately my experience on the forums and also with various family , friends and clients
makes no difference really , it all depends on the layout of the property, the construction, the position of the router

But it sounds like you may have had a duff tablet