Thanks. Am looking at a 109Mb FTTP.
I did just whatsapp him for clarification...
"ISPs have to supply their own core (pipes to the internet). Openreach just gives ISPs access to the pipes that go from exchange buildings into homes. PlusNet is part of BT so has access to BTs (superior) core."
Your contact has better clarified what he meant by core network in the text above.
For your average consumer even those buying higher speed FTTP services, the quality of the core network is very unlikely to influence your experience. Gamers might look for slight differences in round trip times to certain hosting endpoints which is influenced a bit by the core network, but in reality any differences are marginal for most consumers. I would suggest that the difference in the "core" will really impact enterprise customers who will leverage additional services to differentiate and separate traffic flows. But this is where the big money is, there's little or no profit from consumers as far as the core network is concerned other than to soak up capacity.
For your average consumer I would suggest the things that matter beyond common sense stuff like good day to day operation of the network are
1. whether an ISP has oversubscribed and oversold the available bandwidth from an area to their core network (some provide their own circuits, others opt to use BT Wholesale), and
2. the ability of their support operation to help customers with queries and faults - the main difference here is whether they read off a script or have genuinely clueful people on the end of the phone, the latter being rarer these days, and
3. the quality of the router the ISP provides and whether it supports WiFi mesh networking.
4. Other services that you might want to bundle with broadband, digital voice, content, etc. will also influence the value proposition.
So it's probably fair that your BT bigwig is aware of the ongoing investment they are making at a board level into their core network and how this will influence the BT Group to make money, but I think he's overstating the case that whichever core network you use really makes any difference to your average consumer.