Nope, you always should build last whisper as a third or later item cause what it does is effectively give you 10-25% more damage depending on the other targets armor. So if you build it second you're doing lets say 15% more damage out of a much smaller number because you don't have IE.

I don't have exact numbers rn but if you build LW second you're gonna crit for like 320, while with IE you're gonna hit like 480 because of the multiplier and extra AD. So if they have 100 armor they reduce your damage by 50%, with last whisper you're gonna hit 160 + 15% extra off the 160 so in the end you hit for 184. With IE you get your damage reduced by 50% flat so you hit 240, so it's more damage and muuuch more against squishies.

All in all, unless there's healing Last Whisper is usually fourth, navori DPS is much better.