Light Zed is indeed annoying, but unrealistic to actively go for.
Senna on the other hand is a unit that anybody playing Lucian will want & she honestly should've been Light to begin with. Design fail right there. Light is a trait that benefits everyone for each Light on the board, even dupes are very useful.
With the addition of Lunar, team comps get 2 units tighter. You speak of "planning for 8," but you need 6 Lights for the useful Light trait, 2 more slots for Lunar & 1 more for Soulbound makes 9 slots & I ain't even mentioned Zed yet.
That isn't even mentioning the damage changes made several patches ago to increase early-game damage. Light tends to struggle before it reaches 6 Light or 3+ Lunar. Unlike last season when you could hold out just long enough to see Kayle, you're more likely to end in 8th place if you're holding back, intentionally waiting for both a Talisman & a tier-5 unit.