I had recurring deep and paingful acne since the age of 11, but I never saw a dermatologist after I had one horrible experience when I was about 13. So when I finally saw a derm at 16, I was told that I had grade 3 acne and put on isotret from the get-go and recommended chemical peels because it was mostly past the point of topicals (I had tried salicylic acid several times, old derm had given me adapalene which didn't work, bpo was causing chemical burns if used as anything more than spot treatment). I think the decision to avoid tretinoin was because of my age (this kind of awareness about skincare among teenagers wasn't very common 3 years ago) and in hindsight I'm thankful for that since I would've gone ham with it and ruined my skin (plus I barely used sunscreen despite my derm insisting on it)

I was on a low dosage of isostretinoin for about 2 years and it has helped a lot with my acne, though I still struggle with hormonal cystic acne that I'm trying to treat using OTC topicals.

I think your dermat is rushing into isotret unnecessarily if you yourself say that your acne is mild, I would get a second opinion if I were you