Does lulu Help pix bonus magic damage per auto attack actually help adc?

Every time I always shield my ally adc with help pix I always wonder am I giving decent amount of bonus damage to my adc in other words is it helping at all. I always look at my adc magic damage and see its always very small. I was wondering if someone can do the math and explain to me the damage output of pix and tell me if its actually good.

Lulu passive: Whenever Lulu or the allied target of Help, Pix!.png Help, Pix! attacks an enemy (excluding structures and wards), Pix fires a barrage of 3 homing bolts toward the same target that deal 3 / 7 / 11 / 15 / 19 / 23 / 27 / 31 / 35 (+ 5% AP) magic damage each to the first enemy they each hit, for a maximum possible 9 / 21 / 33 / 45 / 57 / 69 / 81 / 93 / 105 (+ 15% AP) magic damage.

There some things that I found out: 1)Pix has a max attack speed of 2.0 in other words if adc has 2.5 attack speed pix will continue to do damage at 2.0 attack speeds. 2) Pix shoots 3 bolt and each bolt gets reduce with magic resistance separately. I think this explains the early game 0 when auto attacking but I dont know how. I notice that when I auto attack leona u see my ad damage then pix's 3 magic damage are all 0. Its really annoying. 3) Pix's damage is based on user magic pen and most adc will have 0. 4) Its scale with Ap but most support lulu dont build Ability power (you especially see that in LCS)

I know their is so much variable that affects pix's damage but I was wondering if someone can explain to me if its actually a good passive from early game all the way to late game.