I don't understand why people think of Iggy that highly even after last season. Dude didn't manage to slow down any of the players he faced against and Kawhi cooked him easily, dude is basically a bench player that can't get decent minutes anymore. That Curry-Klay-Iggy-Durant-Dray lineup wasn't as effective as it used to be and any effect it had came from playing those 4 amazing players together.
Injuries.
Did you know that Iggy was forcing those games in the Finals. It is like all bad omens came into the Warriors and they began falling down. Iggy injured, Curry still got that finger injury, then Durant then Klay.
So how do you think a defense chemistry can be done with all of that, add up the state of mind they are into seeing their comrades having a bad Finals game.
I am not saying Iggy is worse than Melo and not saying he is better neither but from individual stand point without putting Melo into this topic I can clearly say that Iggy is well beyond his time to make any difference in Lakers. Melo would be team chemistry dude that Lebron loves to hang out maybe, that could be the only positive for him and I think his playing would be limited but Iggy doesn't even have that.
Yeah, chemistry is good.
But as I said here, Lebron aint Kobe. He cannot control the Lakers management that far unless he wants to share his salary with Melo.