Of course could be one of those coincedences, that I disabled bluetooth at the time the network just got better anyway, but that is certainly what seemed to fix it.
And in fact, just now I tested it again with the pi zero in access point mode and anecdotally, connecting to it to access a python flask web page was not really working when I had bluetooth enabled, disabled bluetooth and rebooted and access to the web page was OK.
fortunately I have found my old usb gps and so no need for bluetooth again.
But doing some background reading on hacking possibilities of bluetooth it seems a bit dodgy anyway if you have a device that is not always connected and someone has been bluetooth snooping and can see the handshake data of that paired device. Don't know the intricacies, not got time to waste on it, when as is often common with these types of things you spend ages working round a thing only to discover it is fixed soon after you get it worked round and so the entire amount of time is totally wasted!!!!
I would suggest that as default in the bluetooth.conf that power is not on, which is the default, but the raspbian supplied config files set power on in the config file as default.
obviously there is a conflict of interests between noobs who might want bluetooth to just work and those who have seen that it impacts on the network,
and this interference might be some known but swept under the rug bug feature of an early version of the wifi chip which could be actually fixed in current zero and pi3/4 ???
Also I am still running stretch, thought I would give the latest release time to bed in.