I feel like this is a common misconception if among people aware of tongue posture, facial development, etc. Technically this isn't wrong but you have to be careful with how you say it. Chewing itself does not cause jaw problems, a recessive jaw from lack of tongue posture does. It's only in conjunction with chewing are these problems exaggerated. This applies to jaw clenching and bruxism as well; clenching, in my opinion, is defined by the difference in force produced by the tongue and masseter.

If we were to define masseter force and tongue force as values, an equal to value means they are in balance while a greater than value for the masseters is clenching; people with bruxism have a greater than value for the masseters. Most likely they have recessive jaws and jaw problems, only made worse by clenching.

So is chewing necessary? In my opinion no, while chewing is optimal and very helpful towards keeping the mouth closed, it isn't necessary like tongue posture is. With tongue posture, assuming you keep your mouth closed, your masseters will have to adapt to the force of the tongue in order to keep the mouth shut. Contrastingly, chewing doesn't have the same sort of benefit as it's not trying to achieve integrity and proper form, but rather just strengthening the masseters which can help proper form (keeping the mouth closed), which is the trap a lot of people fall into.

Similarly, when exercising in movements like the deadlift, for example, there's the advice to keep body integrity by keeping the back straight, this works the core in order to keep proper form and posture. This is the same with the tongue, you are told to have the teeth lightly touching with the mouth closed while pushing the tongue on the roof of the mouth. In the same way, you can work abs and lower back to help you maintain good form and deadlift you work the masseters to keep your mouth closed; while beneficial, these things aren't necessary.