The VA...the benefits side anyway...wants you to go away/not put up a fight. So they either: don't allow for service connection or they underrate your service connected disability. They are counting on you not putting up a fight. I've been out for 16 years now and I'm still claiming things/battling the VA. If you get denied, appeal. Get more evidence, submit applicable research studies and VA case law, get doctor(s) to submit medical opinion letters. If your appeal gets denied, submit for a higher level review. Again, the VA wants you to go away and is expecting you're not gonna put up a fight.
Here is what has helped me:
-Document everything while you're in. You don't necessarily need to go to the flight doc, but it does help to get documented and makes it easier. When writing a personal statement for each claim, you absolutely should write a personal statement. Because I never went to the flight doc for fear of DNIF, I wrote in each personal statement something to the effect of "because I didn't want to risk a career in flying, I did not go to the flight doc for this condition" in a couple I even wrote, "flight doc advised me not to discuss these symptoms because it would mean removal of flight status". When writing your personal statement, I'm not saying to lie but embellishment can help. Also, research the rating schedule for the condition you're claiming. Bumps from 10% rating to a 30% or 50% rating can be huge. Make sure the verbiage in your letter and your symptoms match up with the different ratings. If you're close to a higher rating, that's where the embellishment might come in. Again, not saying to lie or commit fraud, but you have to fight for yourself and describe your symptoms when they have been at their absolute worse.
-VA docs will diagnose you with whatever you might have going on, but they will not write an "in my opinion" (IMO) or nexus (memo connecting your condition to the service) letter. Go to a private doc for that or there are services you can pay to have that done.
-Speaking of letters...get friends, co-workers, fellow flyers, family, to write "buddy statements" for you. There is even an offical VA form for this. Have them state that they witnessed you have symptoms related to the condition you're claiming.
-Secondary conditions are where you can really do well. For example everyone should claim and get service connected tinnitus. Let's say you get migraine headaches, but didn't necessarily get migraines while you were in. You can claim migraines secondary to service connected tinnitus. There are many many examples of secondary conditions connected to service connected disabilities.
-r/veteransbenefits on Reddit is an excellent source of info. I've used it primarily for my research and help filing my own claims. Have never used a VSO or paid service. There are also a lot of good YT channels. DO NOT pay for a service like VA Claims Insider. I'm not a smart guy by any means and I was able to do all of my claims myself through dedicated research.
-You have to look at researching and building good claims as a second job, it can be a lot of work, but the benefits are worth it. You have to know your condition and related symptoms inside/out, you have to know the VA rating schedule for that condition, you have to know how to write a personal statement, you have to know how to prep for your C&P exam, ultimately you have to be your own advocate.