Hello. I'm very familiar with your symptoms because I also have some of them myself. Good thing we're all anonymous here lol
The dry flaky/oily skin along with the chronic acne, dandruff, Seborrheic Dermatitis , and enlarged pores could indicate an underlying hormonal imbalance. Another possibility could be genetics but more than likely, your endocrine system could have some issues that are causing and exacerbating the triggers in your skin. Hormones like testosterone, cortisol, DHEA-s, glucose, insulin, etc.
I also understand your personal frustrations with diet because although they can temporarily improve our skin, it's not a reversible cure because it only puts the symptoms in remisson without treating the underlying cause(s). It can definitely cause stress because you're constantly worrying about foods that trigger those immediate side effects to your skin.
If you have reliable healthcare insurance, try to consult with your general practitioner and ask if you could receive a referral to an endocrinologist. This type of specialist has more in depth knowledge on persistent skin issues that may not significantly respond well to topical dermatological treatments.
Maybe in the near future, endocrine doctors could also think about exfoliative cheilitis and whether or not it has some correlation with certain imbalanced hormones. Dermatology has been useless for most of us with EC.