Correct. It may be a major centre of operations, particularly for BA, but a hub is an operation designed around substantial transfers of passengers from inbound to outbound.
From LHR's own stats, 2010:
Percentage of transfer passengers in 2010: 35.4% (23.3 million)
Now 35% is not a majority, but it is still substantial. I have never seen a hub defined by the percentage of transfer passengers. The only way such a definition might exist would be an airport which only facilitated transfers. I have seen that on the railways (Cornbrook, Manchester Metro, now has an entrance), but not in aviation.
So considering that the facilities in the terminal exist to enable transfers (airside desks, through handling of baggage and so on), and that a sizeable proportion of people still use them, LHR is surely still a hub.
Just because many people think it is badly designed, or just because transfer between different terminal areas can be a nuisance, does not diminish the fact that it is still a hub, especially T5.