Yes, each T5 gates has around 10 or more arrivals and departures a day, far more than many USA airports, to take one example. Gates change frequently, and when we have had threads on that topic it's not usual to see 4 gate changes in an hour for the same flight - only the last gate will be advertised widely. Experience has shown that the layout of T5, and in particular B and C, means that if you switch gates it becomes very difficult to get people to the right place. There is no option of using the transit from T5C to T5A for example, and some people struggle to walk that distance. Gates can only be allocated when the incoming aircraft is zoning and so BA can / does flip linked flights in order to keep delays down. The main departure screens do tend to say "will leave from T5B" or whatever around 75 minutes to departure.

I don't think it makes much difference to the core issue here since if BA gave the gate number well in advance more people would just get lost with the resultant gate changes. What the system doesn't really provide for is people relaxing in the lounge and not realising that time is creeping on. But it's not difficult, given the 20 minute rule, and that every gate in T5 is within 15 minutes of any location in T5: if you are nervous about this, just leave the lounge at 35 minutes to departure, so long as you are fully mobile.