Even just going by the numbers, Russia vastly outnumbers them: Ukraine's just opened a new front of all things, dispersed their armies out further, they're incapable of really pushing Russia back as we've seen. The last offensive was their do-or-die, it's not going to happen now. This Kursk thing has a real chance of backfiring, too, as plenty of people have mentioned - they've deployed a whole lot of irreplaceable crack troops and equipment in a venture that could likely see them cut off, surrounded, and destroyed, and on top of that it hasn't stopped Russia marching further toward taking Pokrovsk.
Russia’s population is much higher than Ukraine’s, but wars are not won on population numbers alone. If you get to the point where you can’t equip your army with enough weapons, your capability to field capable troops hits a ceiling.
While everyone is speaking about Ukraine running out of soldiers for a while (which I think it is greatly exaggerated and far from happening), nobody mentions that Russia has its own problems when it comes to recruiting troops. Russia mostly relies on paid troops right now, and they have kept raising the salaries of troops in order to be able to keep pace with recruiting. This strategy has its limits, because if they continue down this path of bidding up troop pay to attract new people, the government will run out of money.
Everyone believes that Russia has an unlimited supply of soldiers if they decide to do a mobilization, but why are they avoding doing it if it was such an easy solution? The reality is that a total mobilization is very risky for the Putin regime. Also, there is also the precedent of high paid troops in the Russian military, which makes mobilization much more problematic. People will find it unacceptable to fight for free, while those who volunteered got paid handsome money for the same thing.
A mobilization would also further strain the Russian economy, and would cause a big wave of migration, so it is not a good solution for Russia. The question is, will Russia be willing to sacrifice its entire country and future just to keep a few provinces in Ukraine?
Top-notch western military equipment is great and all, but you ultimately still need people to use it. For all of Russia's losses, they can be replaced, whereas Ukraine's already in dire straits in terms of filling out the ranks.
People keep telling that Ukraine is running out of people to use the weapons, yet they managed to surprise everyone by building up many well equipped and trained brigades to invade the Kursk region. If they were running out of troops, they wouldn’t be able to pull this off.
Do I think this will ultimately come to some negotiated political outcome with Russia (somewhat) going home? Absolutely. That's not going to be a "win" for Ukraine - a third of Ukraine will now be Russian territory, and they'll have lost more-or-less an entire generation of men.
Ukraine is not willing to accept losing territory in a negotiated peace. Their conditions are quite clear, they want their land back to 1994 levels, including Crimea. Why would they accept anything less, after they fought so hard and sacrificed so much?
A "lose" situation for Russia is still leaving Ukraine with more territory than they had initially, at the cost of not even a full mobilization of troops. Yes, Russia has a bloody nose from all of this, no question. But there's zero possibility here of a situation in which Zelenskyy "wins" this conflict. Man for man pound for pound, they've lost far more than Russia has, and they're not forcing Putin's troops home en-masse in any meaningful way.
Russia is losing men and equipment at a higher rate than Ukraine. While the initial stockpiles of weapons were much larger on Russia’s side, the production capabilities of new weapons are a differnt thing. Russia has managed to ramp up its production because it relies mostly on refurbishing stockpiles of old soviet equipment, which is cheaper and take less time than producing new equipment.
The problem with this type of ramp-up is that it will run out of equipment to refurbish (many estimates point to 2025 as the year when they run out of tanks/IFVs to refurbish). After that point, the production of new military vehicles will be much lower, and they won’t be able to properly equip their troops and replace the losses.
On the other side, Ukraine will benefit from a ramp-up in production on the Western side, so while the West will be able to donate more equipment, Russia will be able to produce less. This means that the balance of power will greatly shift in favor of Ukraine.
Add to that the increasing number of advanced weapons that Ukraine is allowed to use now than at the begining of the conflict, and the qualitative advantage will greatly turn in Ukraine’s favor.
The surprise Kursk invasion shows that Ukraine can still surprise analysts, and the fact that they were able to take more land in one week than Russia did in six months shows better strategy and more effective allocation of resources. As for Russia quickly taking back that land and encircling Ukrainian troops, that is wishful thinking on the Russian side. Ukraine is clearly trying to move the new border to the Seym river, where it has destroyed the bridges, making the resupply of Russian troops south of the river very difficult. After those troops surrender/retreat/are defeated and Ukraine secures all the land south of the river, the new positions will be very good for defending and creating a buffer zone inside the Kursk region.