"Too" as a sentence modifier

I was recently having a discussion with a friend on the "sure-thing principle" (not relevant but Google if you wish to know what that is). We were discussing it in the context of a scenario and the discussion ended with my friend stating the following;

The scenario is too simplistic

I argued that the scenario was not too simplistic but simply simplistic. This devolved into a discussion about how to use the word too.

I argued that, in this instance at least, the word too in that sentence changes the whole meaning. If you state

The scenario is simplistic

then what you are really saying is

The scenario is simple and could be more complex.

However if you state

The scenario is too simplistic

then the definition would change to

The scenario is simple and could and should be more complex

My friend argued that the word too does not change the meaning of the sentence at all, and that they are in fact the same.

Can anyone assert which is the correct definition, and why? Or if neither is correct, what would be the correct definitions?

I remind you of Goldilocks and the Three Bears. "Too hot", "too cold", and "just right".

To say that something is "too simple" implies that it is simple in a negative way.

The point is whether simplistic is already inherently negative and hence never needs too or not. The question is: can the sentence be so interpreted that the scenario's simplicity is not a bad thing? See here my attempt:

— Mr Aidolaikyu, I know this scenario is simplistic; but only by simplification could we work it out within the allotted time and budget. I believe the parameters essential to our question (will the reactor vat at Fukushima break?) are all present. As you say, we assume that the secondary chimney is a perfect cylinder; but I can assure you that this does not affect the essential outcome of in a meaningful way. It is simplistic, but not too much so.

— I'm terribly sorry, Mr Yusuk, but I believe your scenario is really too simplistic. You're fired. Have a nice life.

Perhaps too simplistic will be a rare phrase, because something simplistic is usually a bad thing; but I think sometimes it is not absurd to qualify something simplistic as too simplistic. Don't add too when something is simply too simple, though.

Too modifies an adjective or adverb to indicate the quality described is excessive in the context. To describe something as simplistic is to make a general statement about it. To describe it as too simplistic is to make a comment with a particular reference.

Just to muddy the situation, if used in a spoken context, "The situation is too simplistic" could also indicate that you're disagreeing with someone who's said that the situation is not simplistic, and doing so in a mildly childish manner.

A: "The situation is simplistic"

B: "No, the situation is complex"

A: "The situation is too simplistic"