The need for C-17 style capability was proven well before the first Antanov charter! However, and this is heresy I know for an operator, there is no point having a fleet with both 130J AND A400M.
The 130J is an extremely capable aircraft with excellent modern avionics, and has the benefit of already being in service with more capabilities being introduced via the RtoS almost weekly. The A400 has all this to go through, after the political wrangling is complete, and will also arrive with no TAC clearances etc etc. However; the A400 will have a bigger boot! And the whole point of the aircraft is to fit in the loads that the RAF/Army/Navy want to put on board. If the A400 comes on line and Lyneham is shut (bl@@dy he!!, heresy pt2) the only reason to keep the ‘J’ would be the cost of re-training crews to operate another type if the ‘J’ were sold. (And before the uneducated get going, by that point the ‘J’ will have proven itself even to you as well as other buyers.) There is no point having 2 aircraft with such overlapping roles!
Given that we can’t afford flying suits never mind C-17s but still need tanker/troop transport, that’s 2 types.