It was western media that created the impression of an impending counter-offensive that would all but end the war, not anything from Ukraine’s armed forces as far as I know.

Or from NATO generals. At least not as an overall theme, or after actually understanding the situation on the ground.

I'd say western media recalled the likes of Operation Desert storm, generally "it's not a war but a drubbing" NATO operations, then saw the Kharkiv counter-offensive, missed that the fast mechanised advance was preceded by slogging advances until a breakthrough was achieved, and then expected the same thing to happen against the Surovikin line. Ukraine simply does not have the capacity to employ NATO offensive doctrine, more or less "hit the opposing force so hard in the air that they'll find themselves fighting a land war against air superiority on their whole territory".

And the Surovikin line which wasn't even the main obstacle as now transpired Russians had positions in literally every single forest belt parallel to the trenches visible from space. And mines, mines literally everywhere, Ukraine turned towards IR imagining to figure out where to best go through them (mines heat up in the sun and are then very visible at dusk).

Russia, of course, also announced the offensive failed the day it started but that was to be expected.