I do not question your reverence, but objectively that is what your theology implies when it denies the Real Presence, and it is directly condemned by St. Paul:
26 For as often as you shall eat this bread, and drink the chalice, you shall show the death of the Lord, until he come. 27 Therefore whosoever shall eat this bread, or drink the chalice of the Lord unworthily, shall be guilty of the body and of the blood of the Lord. 28 But let a man prove himself: and so let him eat of that bread, and drink of the chalice. 29 For he that eateth and drinketh unworthily, eateth and drinketh judgment to himself, not discerning the body of the Lord.(1 Cor. 11)
Jesus is clearly not bread, gastronomically speaking.
The difference is that the allegorical speach is evident in John 10, while Jesus insists on "food indeed" in John 6.
Christ's institution of Communion was not a reference to John 6. Would it have been the case, Christ would have referred to the Bread of Life during the Last Supper.
At the Last Supper He said, "this bread is My body and the blood of the new testament" and in John 6 he said "the bread that I will give, is my flesh, for the life of the world". Direct match. However, you are correct in a way, because both John 6 and the Last Supper refer to the Cross and not to one another.
I don't read transubstantiation into the Last Supper account, you do
This is perhaps a bit technical, but I don't read transsubstantiation into the account of the Last Supper either. What Christ says is very simple "This is My body". Not a figure of My body, not a symbol of My body, but plain My body. This is Real Presence. Transsubstantiation is not the same as Real Presence, and it is not asserted in the gospel accounts of the Last Supper. Transsubstantiation is one way to explain the Real Presence: how is it possible for the flesh of Christ to look and taste like bread (wine, likewise)? The Aquinas's answer was by making the distinction between substance and appearance, -- transsubstantiation. The early Church was not philosophically equipped to delve into that and did not attempt to explain the Real Presence in any way. This remains to this day the teaching of the Orthodox Church, and it is perfectly fine with the Catholic Church also. A Catholic who denies the Real Presence ceases to be Catholic; a Catholic who refuses to explain the Real Presence in any way and believes in it as a miracle which defies explanation is a fine Catholic regardless.
The scriptural evidence for transsubstantiation is less direct than Real Presence, but if one is looking, he will find it in the road to Emmaus episode: Christ is not recognized in the appearance of the pilgrim (figure of priest) but is recognized in the breaking of the bread offered by the pilgrim. Here we have things appearing one way and being in substance something else. However, obviously, other interpretations of Luke 24 are possible.