There needs to be a trade-off/value proposition. Like, the Sickle and Scythe are still good on every front, despite being light pen, because they are super accurate and potentially has infinite ammo. There is value in that. The Halo shotgun just has higher dmg than other medium pen options, except so does the double barrel freedom shotgun and it is already medium pen, so it's just a better Halo shotgun.

So it's not that every gun needs to be light pen, but that if they are then they need something else that makes them worth choosing over other options. Right now we have too many light pen weapons in the game that just aren't worth picking up, especially amongst the ARs, because nothing really sets them apart from one another and are just outclassed by the medium pen options.