Russia did a shit tonne of work putting in mines, trenches, and structures everywhere. They might not fight for shit, but they can dig holes and place dragon teeth. Doesn’t really require much advanced thought or tech.

That may have been the case in meme-circles, but anyone looking at the war objectively knew it was going to be slower. The Kharkiv counteroffensive only was so brutally effective, because the russian defensive lines were so weak and they didn't have any secodary defensive lines to fall back on. Meaning that once the defense was breached, Ukrainian Humvees could just keep driving and pursiung fleeing russians.

Kherson had a better defense setup, but with the bridges over the Dnipro cut, russia couldn't supply them.

Now, russia had time to create layered defensives and their logistics are harder to cut. The push towards the south is the most difficult offensive Ukraine has undertaken so far, so it's only logical for it to take the longest.

There is also a difference in tactics: While russia employs zerg rushes of convicts and mobilized into fortified Ukrainian positions, Ukraine tries to achieve local supperiorities of firepower and taking russian positions into pockets. That lowers your own casualties, but makes offensive operations more difficult.

Offense has been losing to defensive technology since after WW2 the major exception being ICBMs of course.

I think the expectation was for the counter offense to be fast and severe.

Only if you've been chugging western propaganda. It was pretty clear beforehand, and has been very clear since it "started".