That's an odd take.
Ukraine can absolutely encircle Kherson - there;'s only 1 route across the Dnipro at the moment; if Ukraine control that route, then Kherson is encircled - even if that encirclement is all sat 20km away from the city itself - but obviously, the closer they sit (especially anti-aircraft batteries) then the tighter the noose.
It's not March anymore; and Russia is not, and cannot throw its entire military at Ukraine - unlike Ukraine, who not only can throw their entire military might at Russia, but have massively increased their military might since the invasion started - both in terms of personnel and equipment.
Ukraine ceased to be the underdog, when they had (more or less) halted Russian advances, started getting new recruits out the other end of training, and started getting serious equipment from their allies - AKA, about 3 months ago. Nothing to do with when they started counter attacking, everything to do with when they ceased to be the underdog.