Speaking very generally...
Compulsive behaviors are not always detrimental to the dog. But if your dog's licking and chewing are causing sores or infections on his body, it is an issue. Similarly, fly biting (or tail chasing, or spinning, etc.) is not inherently bad. Basically 1. if it is hurting the dog or affecting his health and 2. if it interferes with general lifestyle and well-being, you should find ways to reduce or redirect the behavior.
Increasing exercise and especially increasing daily enrichment can help tire a dog out, and teach him to occupy his attention with appropriate behaviors. An easy way to increase enrichment is to provide more foraging opportunities (use kibble hunting games, snuffle mats, and kibble dispensing toys). Things like a lick mat can give him an appropriate outlet to lick. Providing a variety/rotation of high value chews can give him an appropriate outlet to chew. And as a last resort, you can have an inflatable donut/cone to prevent him from reaching certain areas of his body. I say "last resort" because it isn't necessarily fair to the dog to simply prevent behavior while not reducing the urge to perform it (ex. "I want to scratch this itch but this cone won't let me! ARGHH!")
Not that this matters, but finding more about your dog's history can at least help you determine where these behaviors are coming from. Unfortunately, it is not uncommon for dogs to develop some compulsive behaviors when they are stuck in a kennel too long, or if they were very lacking in enrichment/activity in said kennel, or in a previous home. Genetics plays some role for sure. The severity of these behaviors also varies. For example, I know some dogs who spin when they are stressed. They don't do it obsessively, but it still comes out in spontaneously during stressful situations (and not all stress is bad stress). Then, I know some dogs who will lick their paws raw. Some dogs also need medication to help with their general anxiety so that these behaviors decrease.
But at the end of the day, your dog is your dog. So it is worth continuing to communicate with your vet, and perhaps a behaviorists as well. Best of luck!
ETA: As an added note, when you say your dog was cleared as perfectly healthy... Do you mean through a general wellness exam or after looking at bloodwork? I am not implying there is anything wrong with your dog. I do think that it is a reach for a vet to 'clear a dog as perfectly healthy' IF there are clearly some nuances in behavior, and if they did not look INSIDE the dog. Many problems don't show up in a dog that just LOOKS healthy.