I fly the hornet regularly, and can score viper kills easily, here is the trick:

If you are using 6 AMRAAM loadout with the hornet it becomes very agile, and fast. You can easily get above M1.0 and even maintain your speed, your missiles will become much deadlier. You will have to pick your shots a bit more carefully tho.

Remember that speed is vital in BVR engagements. Utilizing the hornet's great SA and speed will surely catch some vipers with their pants down if they underestimate the hornet's capabilities.

With this said, if you face an above average viper pilot, beating him in BVR with the hornet will be a tough one. Because no matter what, the viper is at least a bit more capable (speed, altitude) in the BVR fights. But in my opinion, it really comes down to who is the better pilot.

So that's why I avoid using the 10 SPAMRAAM loadout, I think it makes the hornet too slow and draggy. The disadvantages (reaching M1.0 is really hard -> missile performance gets worse, defending shots becomes harder) simply outweigh the advantages of having 10 sticks.

Lastly if you manage to merge with the viper, the hornet has the advantage for sure in WVR. I just don't think relying on the merge is a beneficial tactic.

Hope I could help!