Ukraine war: Putin to boost Russian troop numbers by 15%

No, it's that easy either, because Russia has way more losses than Ukraine. You also cannot just look at raw population numbers like it is a video game where every number represents a potential soldier. There's people who aren't able to fight, there's also people with critical jobs to keep the economy afloat, or even just society or basic infrastructure. Those losses are very significant and will affect Russia for a very long time, hence why Putin called for women to become breeders for the motherland.

No, because will to fight is also a factor. Neither country will fight until the last man standing. Where the cutoff is will vary.

Ukraine's got significantly-stronger incentive here.

For Ukraine, losing the war badly means no more Ukraine.

For Russia, losing the war badly means Russia doesn't lop off part of a neighboring country, doesn't get larger.

Take the US in Vietnam. The US is unquestionably militarily more capable than North Vietnamese forces, never lost a significant battle. However, what dominated in determing the outcome of the war was that the resources that the US is willing to expend on a conflict that is only peripheral to American interests is far lower than what it is in an existential fight for the US. If an invading force were marching on Washington with the aim of ending the US, I'd expect the US to be ready to do total mobilization, to fight a nuclear war, to suffer the destruction of a lot of American industry, to burn through a large percentage of lives. But the interest in Vietnam was predicated on domino theory, a considerably smaller and more-uncertain threat.

There was a famous quote about Vietnam -- not about the Americans, about the French colonial forces, but same idea:

You can kill ten of my men for every one I kill of yours. But even at those odds, you will lose and I will win.

-- Viet Minh leader Ho Chi Minh in a warning to French colonialists in 1946.

Ho Chi Minh was right.

France had double Vietnam's population, and a lot more sophisticated military hardware. But that wasn't the dominant factor -- what dominated was that the Vietnamese cared a whole lot more about being out of the French Empire than the French cared about keeping the Vietnamese in the French Empire.

And Ukraine isn't suffering anything like those kind of casualty ratios and has much more favorable ratio of support and hardware access than in Vietnam.