M&M - Health Question

We’re on our third week of dabbling in Mutants and Masterminds, and our GM is increasingly concerned about the lack of visceralness and granularity in the health system. I’ll see if I can capture his feedback below:

1. It seems too easy to go from healthy to incapacitated. (which is going to be a deal-breaker for my GM - not for his NPCs, but for the players - on principle my GM does not like systems where “at level” one-shots are a probability)
2. It feels like there are only 4 stages of heath (like 4 “hit points”).

So my question is: how “sturdy” is each stage of heath supposed to be? In a balanced encounter, how many rounds (on average) should it take to push an NPC (or a character) into the next stage (assuming there is ramp up as damage does accumulate)?

Now, I suspect part of the issue lies in several factors:

1. Our newness to the system, and the GM setting PL4 generic mugs against PL8 superheores. I suggested to the GM he should tweak the toughness and fortitude of the NPCs as needed to beef them up while keeping them in a PL8 setting. (For context, we are supposed to be the first supers in a world of regular folks, so PL4 NPCs was intentional, but I think that mentally, the GM was thinking PL4 is “half strength” and in a logarithmic ruleset, the PL8 characters are something like 16 times more powerful)
2. Without understanding the risks, the GM allowed one of our players to take incorporeal, and so that character is basically clearing the board with being unable to be touched and having his only two abilities be effect-only “aoe” (one is centered on the character, the other is a frontal cone effect). I assume this is Mutants and Masterminds “Rookie Mistakes 101"
3. We may have coded some of these characters “wrong.” The downside of so much being manual, and one of us actually a coder.

So I figured while we are checking to make sure our characters are within the tolerances the ruleset indicates, I wanted to get a better understanding of how we should expect a typical encounter session to go down if all the characters and NPCs are properly balanced.

As an addendum, I know there are house rules to convert the current health logic into traditional hit points, and I was wondering how hard would that be to code that? I understand you’d likely need knowledge in XML and LUA (neither of which I have), but was wondering what the level of effort it would be to actually create an “add-on” to allow for it.