Natural fruit flavouring just means they have extracted a natural flavour from that particular fruit. But that has no bearing on whether that
juice will quickly gunk your coils or not. A naturally extracted lemon flavour could be used in a lemon meringue pie recipe as an example. The lemon itself may not be the culprit to crusty coils, but the other ingredients used to make that recipe.
Sweeteners can also be used with fruit and or menthol flavoured e-
juice. There are no boundaries as to how sweeteners are used. But from my experience, despite sweeteners such as sucralose and or ethyl maltol do contribute to coil gunk, there are much, MUCH worse flavourings out there.
The general rule of thumb is the darker the juice the more likelihood it will crust your coils quicker. Fruit and menthol juices are usually lighter in colour than their tobacco and bakery counterparts.
I have made the same recipe in different VG/PG ratios and have not noticed any improvement to coil longevity. In the end it is the flavouring of the juice that is the culprit.