Idk, thinking about it logically ignoring a flat 40% seems insanely powerful. Your basically removing half of the opponents defense (to your attacks). Wouldnt it be better to bump it down to 30% and just give each one +10/20 AD or AP
in a gamestate where defstats actually meansomething, you'd be right, but i hardly see LD already cause tanks(if they are played at all) dropp fast enough without the %pen already.
As for void, it's the lategame insurance for AP, they lack multiplicative scaleing like ADs and are more constrained by CDR and mana, so void can be allowed to be that strong to keep them relevant later on.
I almost never build 
in almost all cases 
is just a better option because of grievous wounds.
"Think of all the places this 
can go."
No. They are meant to be tank busting items. You're suggesting making them worse against tanks and better against squishies for which there are already better items.
Why?
Void staff is over stat.
LDR is ok.
LDR/Mortal Reminder should change costs with Void Staff.
Magic Resist is harder to "stack" so the penetration should be more expensive than Armor Penetration.
40% is far too low and it needs to be bumped up to 60% like dawngate.
