Adapting True20 and I need some advice

Basically, it's a sci-fi shooter. The main focus is on the brutality, as it is based on combat sports and corporate endorsements, rather than warfare or any meaningful conflict. It will have pretty much equal parts melee and ranged combat, but my decision to include races rather than use the three roles in True20 is starting to show some flaws. Originally I thought about applying Warrior, Adept and Expert to three races, but now I decided I will have 5 races. One of them is a large creature, meaning it has significant stats bonuses and penalties. These larger creatures are meant to be a bit worse at shooting (though they can dual wield heavy weapons), but fierce in melee. Looking at how the leveling system in True20 features a universal Combat Bonus, I was wondering how I could reflect their ineptitude in shooting and prowess up-close. Should I give them a separate ranged and melee combat bonus instead of the universal one? If so how would I balance it? Should I just give them a universally low combat bonus (to reflect being slower in melee too), and just boost their melee damage? I'm a bit stuck. Also any advice on removing supernatural powers entirely would be greatly appreciated. Thanks in advance.

Try M&M3 instead True 20, M&M sounds better to what you have in mind

Normally you would do it with a ability score penalty, like -2 or -4 dex penalty. So you would probably have stat modifiers like +2 to Str, -4 to Dex, capable of dual wielding two handed weapons. Players can decide if they still want to be a ranged attacker by what class they select and gaining a weapon proficiency with a ranged weapon. Another way you might approach it is to only give weapon proficiencies by race and not give it ranged weapon proficiencies. A player could later take one as a feat though. Just some suggestions.

I didn't think about proficiencies. That sounds like a good idea actually! I wouldn't have to change the way combat bonuses grow as a character levels then. That makes things a whole lot simpler; thanks! I'd still have to think about how to balance the whole thing, but it's given me some direction to look towards.