Either Jesus meant that we have to actually eat His flesh and drink His blood, or He didn’t mean that. Regardless of what He actually meant, these positions contradict each other, so how can we say that they’re equally correct?
As you say, there is room for disagreement both with and without Tradition. I erred in my original argument by failing to make clear why I think disagreement is acceptable when Tradition is present but unacceptable when Scripture alone is in use. Let me try to draw that distinction here; hopefully this will clarify what I had in mind without contradicting my previous statements.
The problem with disagreements that arise from sola scriptura is that there’s never any way to resolve them: If there are two contradictory, but plausible, interpretations of a passage, we have no way of knowing which one is correct and which is not. Since God’s not writing any more Scripture to help us out, these plausible disagreements are areas where God has made it impossible to be certain about His teaching. The concept of God saying, “There’s an important theological truth here, but I’m not going to let you figure out what it is,” bothers me. Why would God simultaneously want us to come to know Him and not provide us with the means to reliably do so?
Combining Scripture and Tradition avoids this problem by allowing us a way to determine what God actually meant. Tradition gives us a living authority, equal to the Bible, that is capable of defining doctrine to settle these disagreements. John 6, taken by itself, may be ambiguous, but if an infallible authority clarifies it by saying Jesus was speaking literally (or by teaching something that demands this view), then the matter is settled. Tradition and Church authority give God a way to clarify His existing teachings so that we can come to know Him better.
So, the short version: With the Bible alone, I have no way of being certain any one of my possibly-false beliefs is correct, and I will never have any way of gaining that certainty. With the Bible and Tradition, I can gain that certainty, because the teaching authority of Tradition can clarify things that were previously unclear. Though disagreement is possible, we at least have a way of (eventually) resolving it, which lets us come to know God with certainty. I have to imagine that a God as merciful and benevolent as ours would aim to provide us that certainty rather than forcing us to wallow in doubt.