Looks to me that this is a complete volte face on BA's part.
Reduced F lounge size with limited hours now replaced with an F lounge on a par with LHR T5 or T3. The Club lounge actually looks like an improvement on the LHR equivalents with the same food and beverage offerings.
I am not sure of the sizes of these lounges. There has been a comment that the new F lounge is larger than the old F lounge on closure. I imagine it is at least the size of the old pre-contraction F lounge. The old Club lounge used to be on two floors too, but I am unclear whether the new one is of comparable size.
One thing I would say is clear is that this represents a very firm commitment by BA to LGW and to the continuation of premium cabins, both long and short haul. I say this as otherwise why have an F lounge and why have such a large Club lounge, if the only users would be status passengers on one-class shorthaul.
Indeed I would suggest that the new capacity is greater than current flights merit. Whether BA have immediate plans for route expansion, the additional lounge capacity would certainly allow significant route growth, particularly long haul, where bar the lack of a CCR, the playing field for ground products between LHR and LGW has been dramatically levelled. In fact, given the normally swift Premium Gatwick security and the noted friendliness and efficiency of BA's LGW staff, provided the location is not inconvenient, then LGW probably has some advantages over LHR now.