There's a delusion here with FF1, the game is fun and ok but that didn't place SNK in the fighting scene, that game wasn't meant for competition, neither was AOF. They were more of a single p[layer fighting game and I say fighting game loosely 'cause at times they felt more like an evolutionary step of brawlers into fighting games, think of it, rigid and rudimentary commands, limited movement, limited control, to me this wasn't it. FF2 and Samsho 1 were made with VS competition in mind, a complete different mindset came to play when those games were designed along with everything that came after.
Those who say KOF was it are either too young or started too late.
As for World Heroes, well it did play better than FF1 and AOF so at least it had that going for them but it was also a bit limited, sorta like power instinct 1, rather odd sprite movement, not the animation but the actual movement of sprites in the screen, some moves were either too fast, too slow or all over the place, nonetheless I do love the Gouketsuji series, love it dearly.
FF2 first game to step it up and compete with SFII maybe even top it but at the same time shortly after the updates started coming along which leaves us with the best fighting games ever; Super Turbo and Fatal Fury Special, everything else even to this day lives beneath them. ST being the pinnacle though, I don't think SNK ever manage to beat Capcom on that aspect, it pains me to say it but I'm doing it with total clarity and fanboy bias aside.