I used to be interested in these events. Over the years I saw that the city already had a very clear idea of what they wanted and used the workshops to direct locals towards that vision. The construction companies have probably already signed the contracts. I asked a question once and the City Hall mandarin stood up, waved his hand and said "We've hired a consultant" and that was the end of that.
The art is being able to discern what objectives the City (or whatever body) is really committed to achieving; whether you agree with those; and then providing input on what IS up for discussion.
You're quite right that often with consultations, government has an idea (sometimes vague, sometimes quite specific) in what they hope to achieve, before anyone submits a comment.
But that doesn't mean you can't influence things.
Lets take Market Lane Park.
There is a clear notion that the City has around its relationship to the new North Market. The idea of the latter being able to spill out onto and animate the former.
If you oppose that idea, then you probably won't get too far, unless your opinion is widely held.
But if you're fine w/that, there is certainly room to discuss the 'how'.
How many trees, or flowers or benches? What style? Could we do hydronic heating so as to eliminate the need for salt, and reduce the City's liability risk (slip and fall).
Will the trees have enough growing space? Could we look at native perennials in the display beds? How will the design relate to St. James Park across the street?
There's still room to affect change within the broad parameters of what the City hopes to achieve.
*****
Its no different with bigger projects. On Queen's Quay East, I was one of many who spoke/wrote about the need for better growing conditions for trees, hydronic heating, and more use of native plants...........
Lo and Behold all of these ideas factor into the approved design.
It certainly doesn't always work out that way; but there is rarely harm in trying; and if you succeed in pushing positive change even 1/2 the time, you're surely making your City a better place to live for you and your neighbours.