TheVaultDweller
Front line cannon fodder
I'm not saying a normal human has any chance of beating one. But exceptional ones don't just get killed instantly. Dutch was getting his ass kicked, but he didn't just get killed immediately, and got a shot or two in. I'd regard Ant-Man as more formidable, based on feats, than anything we have seen a Predator hunt on screen. Remember, he himself easily steamrolled through groups of opponents, and defeated the Falcon, despite not trying to actually hurt him.
Beyond the abilities the Ant-Man suit gives Scott, he was already highly agile and skilled at acrobatics, as well as adaptable and intelligent. He's also a highly skilled fighter. Ant-Man also handled Yellowjacket's weapons just fine, and he had a much greater rate of fire than a Predator does IIRC. Other than the stealth, I just don't see anything for Lang to seriously worry about, and he himself would probably remain in tiny mode until he had a handle on what he was dealing with.