Lucky you
I know you've posted about GWM/SS a lot, and data isn't likely to change your mind. That's okay, because your experience matters more than data. But...apart from the combinations, it really doesn't make that big a difference (tables from Xetheral on GiitP):
If you're interested, I can post the table for attacks with advantage. In any case, if you have a baseline 65% chance to hit, you're on the "8" row (assuming you're keeping up with your attack ability score, in addition to taking the feats). If you have Archery fighting style, you're on the "6" row. So, anyway, I don't think it's that I'm "lucky," I just think its okay for martial PCs to take a feat that allows them to do a bit more damage with their heavy weapons and longbows.
Anyway - how does your Shield Brawler and Thrown Weapon Master feats work?
Shield Brawler
You are trained to use your shield as a weapon. You gain the following benefits:
• When you are wielding a shield and take the Attack action to make a melee attack with a weapon other than your shield, you may use a bonus action to make a melee weapon attack with your shield that deals 1d4 bludgeoning damage. (Crawford Note: I don't give a rat's ass whether you take this bonus action before, between, or after your regular attack(s).)
Thrown Weapon Master
You are exceptionally skilled with thrown weapons. You gain the following benefits:
• When you make a ranged attack with a thrown weapon, the weapon’s long range is doubled.
• Attacking at long range does not impose Disadvantage on your attack rolls with thrown weapons.
• You can draw a thrown weapon as part of your attack, without using your free object interaction.