From a historical lens, it is obviously not the same teachings Jesus taught or even James his successor or Paul who created the first layer of orthodoxy that won out eventually (eg, Christians don't have to be Jews).

But you can't argue that it isn't correct because it's not historically the same, they're just arguing that it is religiously true. That's like arguing that a 3-sided shape isn't a square because it's blue, you're right but not making the right argument.