I agree with you that Jesus was trying to correct them from a crass naturalistic understanding of his words here. (And that’s the key distinction here we need to make. It’s not just that the Jews understood him literally, but
naturalistically. Catholics take Jesus literally, but not naturalistically.) They thought that he meant they were going to eat a dead body, he’s telling them that his body is going to be glorified and he’s not going to be dead. The way they will eat him will be in a much more glorified miraculous way than they are imagining.
But, it still doesn’t follow that all he’s talking about is believing. I still don’t think the context supports that reading. He made it abundantly clear that we do have to eat his flesh and drink his blood. But just because we aren’t supposed to do that in a cannibalistic way, does that mean we don’t actually have to eat him at all? I don’t think so, and here’s why. The Last Supper.
It’s really a bad idea to try and read John 6 in isolation from the Last Supper accounts. Because both are connected to each other and both shed light on the other. I know that that article you linked us to tries to say that the two have nothing to do with each other, but I find that odd personally. Both take place on Passover, both have Jesus commanding his disciples to eat his body and drink his blood. There’s a reason that Christians throughout the ages have always seen a connection between the two.
Anyways, at the Last Supper, Jesus shows us exactly how we are supposed to eat his body and drink his blood. Not in a cannibalistic form, but under the form of bread and wine.
I think this changes everything. Because if John 6 were it, and Jesus never went on to do what he did at the Last Supper, then we would be forced to interpret Jesus’ words symbolically. There’d be no way we can eat his flesh now. But because of what he did at the Last Supper, that sheds a whole new light on his words. We do really have to eat him, but it’s in a miraculous way no one could have imagined.
Now I know you disagree and don’t believe Jesus was speaking literally at the Last Supper, and we’ll get to that

but for now do you see what I’m saying? That by saying what he did at the Last Supper, he was revealing exactly HOW we were supposed to eat his flesh and drink his blood. That means he was talking about more than just believing in John 6. We really do have to physically eat and drink.