Short version:
It looks cool, thats about it
PDL is generally a joke in ROTR, dont get me started on it...On paper its that ECM's can spread the damage to your other tanks when it deflects and that Arenas explosions damage allied or hostile infantry but the games flow never goes in a way where either are relevant in gameplay.
At most PDL for USA is good for;
TMD PDL is good for: God knows??? Too inconsistent and too slow
ATV humvee pdl is nice when engaging stinger sites, It'll pdl 1/3 of the missles there.But if you have ATV Humves why don't you use the mortars?
Avenger PDL is good versus some jets, but its fragile so unless its moving it'll be overwhelmed by anything pretty quickly.Avengers survival tool is its speed more then its PDL when engaging aircraft or the sorts.
Paladins actually crush scorpions because they are not meant to engage heavy tanks like the paladin.The PDL just makes their scorpion rocket invalid.But this wont protect you from the majority of flying burst based rockets or multitude style of jet fighters.
In ZH or Generals the PDL was effective against Infantry as it zapped them (Which it now cant and it gets countered by hijackers with ease.Also SHW/ROTR Hijackers dont die when the tank dies so its like a mind controlling terror drone)
So far we have the:
Missle defender =If your using paladins vs another USA then your at tier 2.Upload the replay because USA games are brutal and toxic, they never last to tier 2
Tunnel defenders are units you'll never see at tier two, even with battlebusses due to how common place air is so this wont work either
Panzerfausts can get zapped but at tier two you'll face grenediers more then panzerfausts
RPG Conscripts have an upgrade thats made to bypass your PDL, plus shocktroopers are a good choise.
TL DR:
Paladins "decent" for its stats and needs alot of upgrades to be valid, the PDL is a cosmetic
The avengers speed iand turret turn rate is what sells it, the PDL is there but you wont really feel if your facing a decent player
ATV humvee is already a great unit, this is just something "cute" on it and it doesn't really need to be great
TMD is something you get for the distraction flares, not the PDL,
The other sources of PDL aka the repair drone and cyclops are like the ATV humvee, Its there to be cute but gets overwhelmed all the time
Dont rely on the PDL, the only actual place they might matter is if the USA "deathball of doom" tactic.Where this just helps you keep that death ball alive abit more.
All in all you have nothing to PDL or you have too much