In all fairness, Ukraine was the Soviet Union’s main place for development of weaponry, so as long as they managed to stall Russia, this was always expected to end up happening, especially give that the West isn’t really geared up for a full-on prolonged conflict with a large adversary at the same technological level (for decades the West only really has faced smaller adversaries with weapons two or more generations behind) so it can’t actually supply advanced weaponry to Ukraine in enough quantity without depleting its own stocks, meaning that any help will be front-loaded (with weaponry taken out of stock and mothballed systems) and then the quantities will become less as the stocks deplete and its Western production ability that limits them.

So Ukraine knew they could only rely on Western weapons as long as the stocks in the West didn’t got too low (because the West couldn’t produce them fast enough, not least because it had gone down a direction of highly complex hence costly and slow to make weaponry), they had some general know-how of weapon systems development and manufacturing from back in the day and they still have the quality of Education that means the still train people perfectly capable of designing their own systems using the most modern software and hardware.

And then, of course, they’re in a position to quickly test and improve against a sufficiently advanced adversary anything they develop.

It always made sense that Ukraine not only should, but could follow a mid to long term (couple of years) strategy of developing their own systems optimized for their own situation not just militarily but also in terms of cost and manufacturing capability, and that seems to be exactly what they did.