More capacity does not directly translate to a better quality product, in the same way that more expensive does not make a product superior either.

What is inferior about the Tesla charge controller specifically?

You again assert that this product is mediocre, and so far have only offered less battery capacity and price as the primary examples. I have countered with more support, functionality that would not exist in a home built system, and peace of mind when it comes to insurance and liability.

The last bit alone is huge. One mishap can result in an insurance claim that could leave you on the hook for the whole house if they deny it.