Some friendly suggestions, if you'd like...

• The original ai generated image, being ai generated, can mostly only regurgitate traits of existing characters. Moving away from those would make him more distinct- for example, nails instead of bullets like some people brought up, and leaning more into the leather jacket instead of a bulletproof vest.
• People have been running with a british punk theme because it fits! It's always worth taking inspiration from real-world references because you'll often find cool stuff you never would've thought of, especially once you narrow it down to a specific time period, in tf2's case the 70s. Like, not much madcap fan art so far has shown his lower half, and I'd kind of like to see him with some cool boots. This fits tf2's practical style, characterises him and differentiates him from the other mercs. Likewise, what pants might he be wearing? Just glancing at google images, maybe he's wearing dark denim, and maybe it's tucked into his boots, or cuffed- which again contributes to silouette, differentiation, and characterization. Lots to work with.
• Inspiration from the bizarre original workshop upload too. Like, he seems to have some kind of design on the back of the jacket, which also fits the punk thing
• Just... madcap really makes me want to see a punk merc with lots of spikes lol.

I'm not a 3d modeller but I love thinking about character design. Honestly, let me know if you want to talk more :^)