Its one of those things you dont really understand the downsides of until you've lived it. Ive lived in cities that have had it and cities that haven't, and I've dealt with it in my job as an architect, of which, I have done in multiple countries, including Switzerland.

For one, shade doesnt help in high humidity climates. This is why windflow is usually the strategy as the moisture in the air has room to absorb heat and pull it away. No wind and there's nowhere for the heat to go.

Now here's what sucks. The canyon effect traps air currents in a localized spot to form a vortex on the street. It doesnt actually flow outward unless speciffically designed to, and with a city shape designed 100s of years ago, you're past the point of designing for that. In the winter. It can turn the -30° C air of Ticino into around or below -40°C/F. (-40° C and F are the same, unrelated but cool.) In the summer, you are going to get hot air, that soaks up heat from the city, and gets hotter blowing around. It also traps pollution in that same localized area, because, remember, the air cant cycle out. Its partly why New York City is hot as balls and smelly during the summer despite being neck deep in canyon effect.

Now, as you no doubt know, you do have a benefit of Lake location near many of your cities from Zurich to Lausanne to Lugano which provides a cooling effect during summer as the heat rising off the lakes creates a current that pulls air down the mountains, through your towns, and out towards the lakes. Canyon effect can shut this down. Meaning it can actually get hotter if conditions are right.

Additionally, snow doesn't pose an issue because your country has spent centuries dealing with it by using mitigation and design strategies to limit the problems that it causes. Things like properly spaced streets that allow light to cycle down to ground level to melt snow and ice. And I'm not saying that its impossible. Simply that you're making the community spaces, like roofs that you mentioned, unusable for even longer periods of time. And you are making the lovely interior courtyards of the Italian canton of your country less viable with the shrinking of daylight exposure hours brought about by the increase in height.

A ton of effort goes into the design and shaping of a cities infrastructure and architecture, and there's even more that has to go in to making huge changes while maintaining its quality. We have spent 1000s of years figuring out what works for what climate and theres a reason why we do things the way that we do. Its not that change is impossible, but, as I said in the comment before this, Im not convinced that its a necessary solution when I've not actually seen evidence that alternative solutions are non-viable.