I live in Montreal too, and while all what you say is true ... the same is not true for the xUSSR cold cities I lived before immigration. So quality makes difference. Also planing and designing for less maintenance. Concrete structures from the same era across xUSSR are in way better shape.

Montreal has infrastructure problems because of systemic corruption with the local Mafia.

To think that the USSR had better infrastructure (less corruption) than modern day corrupt places like Montreal is a brutal shock.

Only if you take out the rebar. Concrete is porous, water penetrates to the rebar inside, the rebar rusts and expands, cracking the concrete. But if you remove the rebar, you remove much of the tensile strength of the structure, which means you need to use way more concrete to compensate (via the sheer compressive force of its own weight).

What about those new materials for rebar? Like fiberglass? What do you think of them?

Not the parent. My understanding is metal rebar is the cheapest. You need a lot of rebar in modern concrete construction.