New Zealand is sending troops up there to train Ukrainians on the artillery. Knowing our Government, they won't be going in-country, but it is likely going to be done somewhere like Poland. It takes away another target for the Russians.New weaponry is exactly stuff like the 777s and other guns coming in from other countries. Couple of weeks to pull crews off for cross-training, and I bet setting up logistics for the new ammo and such requires a little time too. I don't think t's as simple as "here's a gun, now shoot it".
Granted that small arms are easily transferable, but even APCs require a supply chain that Ukraine may not have in place.
It stands to reason that integrating this new (to them) stuff is not going to get a Star Trek matter-transporter solution. And that means that they are right now fighting for time, to get sufficient numbers to the front lines.