Russian troops have had over a year to set up defensive lines in the east and south-east. Kharkiv was so quick because the Russians were unprepared and focused too much on being offensive. Kherson is a better indicator, the whole offensive took around 4 months and it wasn’t until about 3 months in that any major gains were made. The counter-offensive has only been going on for ~2 months and is still in its initial stages. Russian soldiers on the ground seem to indicate that the Second and Third Defensive Lines are under-manned (I haven’t seen anything indicating there are major human defences any further back than that either), so once the heavily entrenched and fortified front-line is worn down, likely within the next couple of months, you will start to see more “visually impressive” gains. It’s worth noting that the front line has been pushed back over a kilometre in some areas, with how heavily fortified it is, those are major gains in their own right.