I'd agree that Russia is winning currently, if only on a "possession is nine-tenths of the law" basis that it's occupying a huge amount of Ukrainian territory. But it does have finite resources: it cannot replace much of its best equipment at the rate it is being lost, it evidently has ammunition supply limitations, and more mobilisations and casualties may start testing its population's patience.Isn't it? It's a slower zerging than originally planned but still, it's a relentless advance. Even if the proportionnal costs are high on the russian side, they have overwhelming resources and no loss in them as their territory is unaffected.
The interesting point will come with Ukraine's apparently incoming offensive. If this were a success and recovers another large chunk of territory (e.g. most of one of its occupied oblasts), Russia will be in a very difficult position: it would suggest that Russia cannot expect to hold those remaining provinces because its military isn't up to scratch. It might have huge amounts of manpower, but if it can't train and equip them properly, they're just casualties waiting to happen.