Ukraine has attempted attacks before, yes. Relatively small scale actions on the tactical level. Those weren't offensives. Kherson and Kharkov now are offensives - maneuvers on a very large scale on the strategical level. And this is the first they've put together since this war started and no matter the losses in Kherson, they still managed to collapse the Kharkov area because of it.
This is a massive win for them on the strategical level, not a simple PR win. No other way to frame it. There's absolutely no indication that Russia can or will make the big moves and sacrifices to return these places, despite the massive effort over months to take them in the first place. Izyum was one of the primary objectives and wins in the first phase. It was lost in 2-3 days. I also don't see any reason why the Ukrainians should be unable to sustain. They managed to sustain in these places initially much longer than the Russians now did. They're sustaining all along the front and they've even gained offensive capabilities.