First, you need to read that language very thoroughly. You are missing something in there from what I read, that being that "the subject matter thereof" relates to the claims contained in the "SETTLEMENT AGREEMENT" and does not cover exhaustively ANY of the parts of subparts of the original K because they are not addressed in the "SETTLEMENT AGREEMENT." What you quoted is just a standard language for an integration clause, and only relates to the "SETTLEMENT AGREEMENT." That boilerplate is in any K you will read today. In fact, you'd be disbarred for failing to include it. The other thing of note in that is integration clauses can be, and are blown thorough by courts, so I don't think that is the hurdle you appear to believe it is.
Secondly, The K claim is based on the original K and not the settlement. Again, there are multiple theories involved, not all of them involving the operability of the settlement agreement.
Also note, all of the other theories clearly do not have to get passed the settlement agreement, namely, the theory I put forth here and ever enshrined in the Sixth Cause of Action. There are others.
Lastly, you should be well aware that complaints don't "gloss over" things. We don't have fact pleading like other countries. Sure the Iqbal/Twombly standard in real practice requires more than notice, but any complaints that specified too much detail on the facts upon which the theories of the case are based would be grounds for ethics charges. Incompetent representation is not a good thing. They left a lot of detail out of their COMPLAINT because that's their job. You don't show your whole hand in a complaint. Where are you getting this "gloss over" theory?