Low Church people have not traditionally denies the Real Presence - they have understood it in a way very similar to what one sees in the Lutheran or some Calvinist groups. There are certainly some differences especially in the latter, but they are rather subtle points and not really that close to a symbol only POV. (As in, what does it mean to have what St Paul describes as a spiritual body, and in relation to that what does it mean to say the Eucharist is spiritual.) And I would say that traditionally Broad Church people have said the same things as the high and low.
The modern phenomena of people claiming a symbol only understanding is modern, and probably springs from the same place as the modern Catholics who also believe it is only a symbol.
Have the old broad churchers morphed into the modern “liberal” Christians? I think that their congregations have to a large degree, but that doesn’t mean that there isn’t a clear change between the two groups. The Broad Church people did actually recognize the same kinds of limits on what it is to be an Anglican as other Anglicans did, whereas modern liberal Anglicans do not. Those people are indeed very like Unitarians in their outlook, or perhaps Cafeteria Catholics.
Edit: the problem I think is you are trying to place modern Anglicans into those three groups, and it won’t work. What you will find is that you now see traditional high-church Anglo-Catholic, liberal high-church, traditional low-church, liberal low church, evangelical, and middle of the road liberal. The latter are those who used to be broad, and I don’t know if there are many old-fashioned broad types. A lot of the old low types are now evangelical, and they tend to be almost like baptists or congregationalists, and sometimes don’t even use liturgy.
And in fact they can’t all hold together under the same umbrella, which is why Anglicanism is in the process of re-arranging itself. But a lot of those groups simply don’t correspond to any kind of historical Anglicanism.