This isn't terribly different than the latest precision medicine in the US. For example, drugs like Keytruda can only be used in the presence or absence of cert

This isn't terribly different than the latest precision medicine in the US. For example, drugs like Keytruda can only be used in the presence or absence of certain genetic markers in the tumor. Most cutting edge immunotherapy is similar; they require patient specific diagnoses and sometimes revisions. These therapies are the largest focus of cancer research in the US right now with enormous funding behind them, despite having the same weaknesses you point out as bacteriophages.