The second sentence is just wrong, or ill-formed.
(Exception: you are a playwright or poet and you misuse or re-frame words on purpose.)
sich von etwas verwirren lassen = get confused by something
As for your question whether the first sentence (which is well-formed) carries a nuance of 'unwittingly' or 'at the mercy of': I would say getting confused is per se unwitting, isn't it? Perhaps you wanted to point at possible differences in meaning of
(1) sich von jemandem verwirren lassen
vs.
(2) von jemandem verwirrt werden
Here, I would agree that, yes, you could argue that (2) is more like a neutral constatation whereas (1) has some ironic undertone.
But on the other hand "von jemandem verwirrt werden" is just a little bit awkward as a construction, perhaps due to the odd repetition of sounds:
Der Tourist wird vom Straßennetz verwirrt.
You somehow would avoid such homophony, at least in contexts where some attention to language is desired, e.g. in publishing. Unless you are a poet and use it for a purpose (for example in order to wittingly confuse your audience).
It is more common to say
Der Tourist wird vom Straßennetz verwirrt.
or, best solution in neutral contexts:
Der Tourist findet das Straßennetz verwirrend.
Note, however, that 'die Vielschichtigkeit der Stadt' is something quite different from 'the maze of streets'.
