This is unfortunately just the reality when we’re dealing with organisms with orders of magnitude faster reproduction and selection than us. Maybe the proposed bacteriophage treatments will be better since those can evolve too, but we’ll probably still have to constantly engineer them otherwise we’ll get periods when bacteriophages work and periods when it doesn’t, not to mention the extremely slim but never actually zero chance that bacteriophages will figure out how to infect eukaryotic cells from the billions of close contact with animal tissue when we actually start using them as mainstream medicine.