What are these better planes that you speak of at Heathrow and what makes them a better plane in your eyes over the Gatwick based 777's?
As others have mentioned the LGW 777 3 class cabins have had a complete refresh in the past 12-18 months. Brand new IFE, USB charging, brand new seats in WT/WT+, mood lighting. What's not to like?
Also you don't mention which class you're travelling. You also mention "we". Is the price you've quoted in your original post total for all passengers travelling or per person? It's difficult to work out your expectation is without the full background.