Why Force Shield and Protection are a waste of points

[WhoIsThis]

So my recommendations would be to use Scenario 4 or Scenario 2. These use 2 and 5 skill points respectively, and will offer you either 60 or 90 mana per minute. This will allow you to spend these points on better DoT or healing skills that will really help you. (and honestly, if you use a couple powerpacks here and there, whatever).

The problem is that you are assuming that the shield will last for the full duration. At shield level 1 on a guardian run, that's pretty improbable. I suppose that the incentive to add more shield points is that it can last a bit more. Whether this justifies it though is open to debate and probably depends on player preferences.

Protection though I think is not worth it. It offers little protection against what it needs most - high burst damage from Vulars and bosses, despite the slope scaling. Here, shield offers at least some (albeit limited) protection. Against ordinary mobs, who don't do lots of damage per hit, but swarm, leading to multiple low damage hits, the 1-2 less damage per hit will have a noticeable effect. But as mentioned before, against those opponents, you really don't need protection because you have time to react. Against things like the Vular though ... it's another matter. Deaths can be extremely rapid, and here 1-2 damage isn't going to make any real difference. Against mobs though, it can be helpful. The real question is, does it justify sacrificing points elsewhere? Imo, no. I maxed damage output because the longer an enemy is alive, the more damage the team sustains.

Edit:
@ OP:
Armor DOES scale as you add more. It's just that you have to add so much armor that you need to add A LOT of armor in order to see a visible effect. Protection the problem is, only adds 60.