Well i made the experience that especially against swarms the Han plus gunner plus marksmanship combo is better than anything else. If i want assault missiles with that i'll just swap an X for an A.
I understand that gunner is not as good against other rebel lists, but against swarms or even stealthed up imperial ships with multiple actions, it just gives you the punch you will need to get that desperately needed hit on Soontir for example. I find assault missiles too much of a gamble on the Falcon, and i often play against those super tough to hit lists with Dark curse, Soontir with PTL and all of them stealthed...
Therefore my experiences go exactly the opposite way, assault missiles have often missed and gunner won me a lot of games.
But the one upgrade that has never ever served me well is the mercenary pilot. Even 2 points is too much for only range 3. If i really need critical hits i would rather take marksmanship which is surprisingly reliable.