There might be no NATO troops on the ground but it's a bit of a stretch to say that it is purely Ukraine vs Russia.
And without the navy Russia annexed [1], or it’s Soviet military kit, much of which was designed and built in Ukraine, Russia wouldn’t have much of a start.
Ukraine repelled Putin’s forces on its own in the early days of the war, when Western intelligence was predicting another Kabul. That it later attracted sympathy is further testament to its diplomatic strength (and the Kremlin’s isolation).
"On 8 April 2014 an agreement was reached between Russia and Ukraine to return Ukrainian Navy materials to Ukraine proper. The greater portion of the Ukrainian naval ships and vessels were then returned to Ukraine but Russia suspended this process after Ukraine did not renew its unilaterally declared ceasefire on 1 July 2014 in the conflict in the Donbas."
[1] - https://en.wikipedia.org/wiki/Black_Sea_Fleet#Russian_annexa...
Ukrainian military spending: $5.4 billion
I have serious doubts the outside world dumped more than $5 billion on Ukraine's side. Russian made a serious error in how much territory they tried to hold as opposed to the re-positioning / fighting over Donbas that's happening now.
If the US ($801 billion) tried to conquer Canada ($26 billion), I would expect a similarly poor outcome based on Canada's size. If the US tried to annex specific oil rich areas under the guise of "protecting" oil pipelines, it's be reprehensible, but so was Crimea.
This means a large portion of Russian military spending can't be used in the current war. OTOH, almost every Ukrainian military asset they have was acquired with an eventual defense against Russia in mind so they have a much better rate of available fighting power per dollar spent.
They did send about $5 billion worth of equipment. It is probably a factor why Russia isn't currently sieging Kiev.
https://www.politico.com/news/2022/03/22/ukraine-weapons-mil...
[1] - https://edition.cnn.com/2022/03/15/politics/biden-ukraine-ai...
That's a pretty basic idea in international politics, having been developed over decades of similar proxy wars. Same reason the US didn't consider itself at war with the USSR in Korea or Vietnam.
Don't underestimate the massive value (and massive expense, for NATO) associated with providing that intelligence. Ukraine is basically playing Starcraft with a "disable fog of war" cheatcode activated.
It's also something that has established precedent in the proxy conflicts I mentioned before, with the USSR and US both in turn providing strategic and in some cases tactical intelligence to the other side. As long as the aircraft gathering the intelligence aren't flying inside the battle zone.