The way I read the VAR situation is that it only reverses a decision if it is 'clearly and demonstrably' (I think was the expression) wrong. It's not simply a matter of judgement by the VAR ref. I can see a difference even if that, in application, it means its scope is quite limited.
For Iheanacho's 2nd, it's application is clear and was perfectly demonstrated. With the Iborra 'penalty or not' decision, it's not a clear cut call, it's a matter of judgement and in application VAR's role is not to disagree with the ref's judgment but correct a decision if it is demonstrably wrong.