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This is a fairly common theory and I'm not sure what I truly think of it yet, I'm going to do another burn through (unfortunately my 3rd) soon.
The Didact is different though. I think that since the Librarian set in motion the genetic eventuality I think that rather than the Didact she created something the Didact couldn't predict or stand against because she also set up Halsey and Cortana. It was inevitable that her and the Chief would wind up together, and its not over. I'm not sure what will happen now that Chief has been stripped of his armor (still not sure how I feel about that, seeing his eyes was weird) but I think he may have the chance now to rise farther than the Didact. However if they start giving him the same Force-like powers I may be...done.
Perfection is a lifelong pursuit requiring sacrifice. The only way to get it quicker is to sacrifice the most.