Whilst I can't fault your tyre choice, your tactics for changing them may have room for improvement. If you'd swapped the back for the front around the 3000 mile point, you could probably have reached 7000 miles before replacing them. Unless you ride very differently to me, the front tyre will still have little in the way of wear after 5303 miles. If you put it onto the back after 3000 miles it will be like a new tyre on the back and a lightly worn one on the front.
It isn't just wear that determines a tyre's useable lifespan, as UV ages tyres considerably - being a major factor in the 'perishing' process. This is why, if possible, you should store your tyres in the dark.
On the subject of graphene, I'm even less certain about the benefits than you. The claims are that it improves grip and puncture resistance. I have Vittoria Zaffiro Pro tyres on one bike, and Vittoria Zaffiro Pro with graphene 2.0 on another. Can I tell the difference? No I can't! If I ride like a hooligan on the empty country roads, (my default style), I can induce lift-off oversteer on both types of tyre. (It is an endearing feature of Vittoria tyres that they are happy to tolerate the use of opposite lock steering mid way through a bend.)
I haven't fitted any new tyres since I got a GPS device to accurately record mileage, so I have only a very rough idea of how long they last. I have a pair of Vittoria Rubino Pro racing slicks (not with Graphene) to fit next year, so I should be able to record accurate mileage figures for them.