The question correctly grasps that an affordable housing program doesn't benefit the wider population of households until it is large enough to impact the market. The inclusionary ordinance will benefit some but not many, and, depending on numbers, could aggravate the squeeze on households in the middle. The ordinance's largest impacts might be unstated or unforeseen.
The new ordinance is not the only tool operating in Evanston. Because a consistent problem with affordable housing is keeping it affordable after its initial subsidy, one I've supported is the community land trust model, which in order to have the wider impact your question gets at, needs to operate on the scale of a couple hundred units in a city Evanston's size. Ideally, housing for lower-income brackets are widely and equitably dispersed rather than concentrated in one neighborhood, and Evanstonians of varying income levels live as neighbors.
I agree that desirability will be the prime driver of real estate prices, which in turn drive one side of the tax equation. All these issues are delicate and have flipsides and interactions with social factors, markets seek corrections, and attempted government interference one way or the other can contribute to bubbles and busts. I don't want to make Evanston more affordable by making it less desirable, and a rash of foreclosures is a terrible way to bring prices down. Because university towns in general often have the desirability drivers, it becomes even more incumbent on our local taxing bodies to seek efficiencies. There is a "soft bigotry" to overspending that, long-term, will contribute to a natural tendency toward both more expensive housing stock and a population that can afford that.
Regarding alternative strategies, Smith wrote:
Not so much "dislike" but data. TIny homes require zoning/code freedom difficult to implement amidst 9,550 pop./sq.mi. (I would consider pilot zoning for a tiny home cluster in appropriate site); not opposed to SROs but need more data to see if Evanston is doing more or less than its share; height/density doesn't necessarily lower prices and doesn't do so uniformly, and land costs are a fraction of unit price in large multi-unit, so question begs premise; ditto parking requirements, unless coupled with enforceable covenants; re tax burden, goal is to lower not to spend MORE on housing but to have more to live on, period, if the market compensates for lower taxes by raising price, housing is not any more affordable; training per se doesn't increase income or lower housing cost, and you have to have the job that is trained for.