I think you are too highly tying a developer to a specific technology. Asking which one you are closer tied to reveals some inexperience in your product manage

I think you are too highly tying a developer to a specific technology. Asking which one you are closer tied to reveals some inexperience in your product management role. Yes there is always a cost to finding new developers and having them ramp up on the codebase. And some of this can be mitigated by hiring developers who are familiar with the stack you've chosen. However the ROI you will get hiring a good developer who needs to learn your stack is much higher vs a mediocre developer who is familiar with your stack.