Bug fixing does not work that way really, especially if you have complex code which can work in very different ways.
What she did is fixed thruster control, AI is now correctly using it. However, it exposed issue in other part of the code.
As for 'why it takes so much time to fix', first, it is behaviour change, not a bug in a code. So it means change something in *configuration* part of code, not *processing* part of the code. That means basically changing it for all NPC AI in the game. Now, that's quite a huge change to be done without extensive testing. It can be done as part of minor release, but it also might be delayed, especially if slowing down as advised mitigates issue somehow.
TLDR you can be angry, but to call devs incompetent I will ask for clarification and on what basis you make that assumption.