Opto-isolator/ optocoupler for electric isolation in IC design
Question
The OP read the following advice:
&quot;Opto-isolator is not recommended for electric isolation in power applications IC's mainly due to it's dV/dt sensitivity&quot;
He would like to know the following:

How dV/dt sensitivity affects isolation?

Is dV/dt sensitivity the only reason to avoid optocoupler especially in power application IC/embedded systems?

Are there other limitations in optocoupler which compel one to chose other isolation techniques?



Answer

I am trying to give answer by referring to the Vishay 4257 optocoupler. I have summarized important points in the appendices below.

I skimmed my summarizes and found that there is only one point I should dig deeper to know more to answer the OP's question.  The other things like high input sensitivity, high isolation voltage etc are irrelevant to the OP's question.
Now the only important point in the datasheet is repeated below:
The ... phototriac uses dV/dt clamp resulting in a static dV/dt of greater than 5 kV/µs.

/ to continue, ...



References
1 VO4257, VO4258 Optocoupler, Phototriac Output, High dV/dt, Low Input Current - Vishay Semi
2 Triac - Wikipedia

Appendices
Appendix A - VO4257 Datasheet Summary


Appendix B - VO4257 Electrical Characteristics