When I started on insulin I was on the maximum dose of Glicazide, but we overlapped them in adjusting amounts to wean from one to the other. I think it was about 3 or 4 weeks before I had titrated the insulin up towards an effective dose and gradually stopped the Glic. The DN did say that once on insulin, the Glic would be ineffective, but would assist for a short time whilst I was on the lower starting doses. As my BG at the time was very high, it was just an additional measure to prevent me going any higher before we'd got settled on a final dose of insulin.
It's very easy to make such comments when your own efforts are still able to make a difference - you must feel that patients on lots of meds or insulin just aren't trying. But for some, it doesn't matter what you do, your BG runs away from you - mine went awry after a medical emergency - I never regained my earlier very good control. I'd managed for around 19 years on diet and my own efforts alone. After the emergency I had 3 or 4 years of increasing meds and perpetually increasing BGLs.
Medics wanted me on insulin 2 years earlier than I started it, but I felt it was accepting defeat and continued to see if I could manage it with my own efforts. Having to start insulin doesn't indicate that the patient is taking the lazy option and has failed to manage it properly - sometimes it does progress beyond responding well to how you manage yourself and you need to accept external assistance.
I wish I hadn't been so stubborn (deteriorating neuropathy made me realise I had to make a change), the insulin sorted it all within a month or two - my doses were pretty small - manufacturers of combined therapies suggest a dose of something like 0.5 - 1.0 unit per Kg of body weight - I was taking 0.28 unit per Kg. I was now free of more side effects than I'd realised were causing me to live in a fog. Ironically, once I'd stopped the meds, my digestive system worked significantly better and I was able to reduce carbs further by eating foods that I hadn't been able to tolerate earlier - like eggs for breakfast. This probably helps me to keep my doses small, although I'm just starting a new regime, as I'd improved enough that the mixed therapy was no longer suitable and my BG started yo-yoing.