The one who provides so-called "help". In the current Russia-Ukraine war, the USA is only providing that much of the weapon which is necessary for them to keep fighting and survive. Not to win the war. Because if they offer them all the resources, they will become a trained force with advanced weapons, which is also will become a threat to NATO. They will become a deadly threat to any other country or system.
That's why most of the weapon provided by the USA is failing too. They are just providing the mostly working weapons. On the other hand, Russia is buying back the sold weapons from China.
If we connect the dots, China and USA are the ones benefitting from this kind of situation.
In principle, we can agree with your opinion. The military assistance provided to Ukraine is untimely and insufficient. At first, Ukraine was helped only by Javelins and Stingers. This, in fact, is a light portable weapon for conducting partisan struggle in the conditions of the occupation of Ukrainian territories by Russia. Because no one, including in the United States, believed that Ukraine would be able to resist Russia for a long time.
Heavy armored vehicles began to arrive at the beginning of this year, and then in very small batches. Moreover, long-range weapons and ammunition are not provided to Ukraine so far. This indicates that the US and NATO want, most likely, to weaken Russia as much as possible militarily and economically, but not completely destroy it, through the hands of the Ukrainians. In such a situation, Ukraine will suffer great material and human losses. The situation is saved only by the courage and professionalism of the Armed Forces of Ukraine.
It is also true that Ukraine received working weapons, mostly of Soviet production. But there are many objective reasons here, since the provision of weapons is late, but they are very much needed at the front. Therefore, they give what is familiar to the Ukrainian military. This is also beneficial for the countries of Europe, because instead of the old Soviet weapons they receive new NATO ones.
But Ukraine is already grateful for the assistance rendered to it. Without it, it would be very difficult to resist Russia.