last whisper still has amor pen

yes, the entire point of it is to counter high armor builds and it also only works on BONUS armor instead of both your base armor and bonus armor. Last Whisper would be absolute garbage if it switched to lethality due to the way lethality works (and lethality as a whole is already a borderline garbage stat to begin with)

The armor pen on LW is fine. Just like Lethality, it means nothing until late game when the tanks have 3 or 4 armor items, and unlike lethality, it doesn't do anything for you against squishies, just like Lethality does nothing for you against tanks.

It's a good antithesis to have, it means that one isn't doing the other's job in the wrong/right situations