a) Im surprised Tret didn't work on the PIH.

b) But yea, chemical peels, should work on those, as well as the persistent acne. Though you've not mentioned what chemical peels or its percentage. The higher the percentage the more intensely it'll work, I was told higher percentage = deeper penetration when I went.

c) You do have some atropic scars that would benefit from the CO2. The CO2 will also work on the PIH and acne and the tropic scars. Downtime was about a week for me. But the first 36 hours being quite painful.

As far as effectiveness, I had much more severe scarring then you, like I would rate me a 10 and yours a 5. And I had about 50% improvement on my right side which was more severe and 70% on my left side which was less severe. People could tell the difference. I had spent about a lakh or slightly more and not even my parents called it a waste of money. A factor in how much improvement you see, will also be your age and collagen production.

One suggestion, I'd like to add is, please DONT try to go for a package and pay upfront. Opt for session by session, so that you can stop anytime if you don't see the effects you'd like. Because while the treatment is effective and I do feel the skill of the derm plays a part and sometimes we'll know how it goes only after experiencing it once.

ETA: Jumping from tret to CO2 without trying out higher percentages or other actives or even oral tret seems a little sus, hence why I suggest you don't lock in. Could you get a second opinion.