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I'm not sure what you think makes the difference between mesh and not mesh, but Sky Q absolutely is a mesh system (although it is not often mentioned publicly) - in an entirely Q setup the TV boxes act as access points, using the same wifi settings as configured on the Sky Q router. Sky also offer "boosters" if the mesh is unreliable, eg in a large house and the boxes can't see each other.

This is why one of the remedies that you often see in those forum threads is where Sky connects one box via ethernet to the router, or installs a booster to do the same. In either case the Q devices can self-organise into their proprietary mesh just as it would if the Q router is used, ignoring the third party wifi network entirely.

You can even enable part of the functionality when using third party equipment - www.sky.com 

I lost some text it seems when I edited, it of course its a mesh system provided by Airties. Yes you can use it as a hotspot but it its basically routing everything through its connection between the Q box and the router where as the Sky router is optimised for that connectivity.