Areas of improvement
That's where his strengths lie; he's an excellent athlete and finisher, and his on-ball defense is something to desire. His flaws are evident as well. But Steve Kerr isn't Spo, respectfully. These flaws would be hidden and improved on in Miami.
Kuminga isn't a reliable 3-point shooter (33% for his career), and his jumper overall could be better. His handle could tighten up to exploit defenders more on his way to the basket. He gets caught ball-watching frequently. But his on-ball defense is similar to Haywood Highsmith in a sense. Long, physical guys that get into opponents causing discomfort. I can already picture Kuminga at the top of the Heat's 1-3-1 zone, causing havoc.
The Warriors are committed to their core trio of Steph Curry, Klay Thompson, and Draymond Green, per reports. Kuminga was starting to get his feet wet over the last month with Draymond out due to suspension. With Green returning to the team soon, Kuminga's minutes may fluctuate again.
If the Warriors don't seriously want to develop a raw talent like Kuminga, sell the property to Spo and the Miami Heat. He will make it work. With the solid foundation Spo has helped cultivate, he can get Kuminga together and have the whole world claiming "he did it again."