That's really no excuse. The US airports have exactly the same system. A new flight every 45-60 minutes. And you can see on the departures board what flights will be leaving from that gate 4 hours ahead. At the gate itself, you will often find "Next flight from this gate [i.e. after the one you're waiting there for] will be Flight XXX destination Xxxxxxxx." And yes, they do have to change gates for operational reasons from time to time, but in the course of a day the vast majority of the pre-programmed arrivals and departures will take place as scheduled.
I say again, it's sheer laziness on the part of BA's schedulers. They simply can't be bothered to plan ahead. Much easier to do it on the fly, but much less convenient for the pax. It's the same thing at Gatwick.
Yes you are absolutely right.
When a BA flight approach LHR the captain already knew which gate he is going and what is the next flight from Dispatchers. So that is at least 30 minutes before landing, the said aircraft knows which gate to park and what is the next destination. The turn around time is between 50 mins to more (So let us call it 1 hour), so that is one and half hours in advance from a flight that Heathrow airport and BA knows exactly which gate it will be.
There is no excuse that BA can not display gate information much earlier.