I've been to a Garden Party and what happens is that the guests (all 2000 of them) arrive early afternoon and have the place to themselves - wander around the garden, have tea and meet people. Those attending are from all walks of life. There is a tendency now to have special garden parties - ie last year there was one for the military and that is the one Harry attended.
Eventually the Royal party arrive and the guests are put into clusters. The royals are "allocated" to a cluster. Certain guests are pre-selected to talk to HMQ but as far I remember that is the only occurrence. Probably only 100 get the chance to talk to a member of the BRF.
The event is for the guests to enjoy BP and does not stretch the skills of any of the royals. It isnt a rite of passage and I think the snarky comments about William are unwarranted.
Thank you for your insight into this "Garden Party" debate. I appreciate your candor and agree some of the comments seem a bit absurd.