I'll meet you halfway though: they should have had profiling sessions that pointed to the JSON parsing code as the issue. I imagine that all of their profiling efforts were focused on the runtime performance, not the load time. Simply put, no one did that profiling, and I don't fault them for focusing on runtime performance (which is where the real money is, as Cyberpunk 2077 demonstrated by not having it, and subsequently having their PS4 orders yanked and refunded).
Once again - Control by Remedy ran on base PS4 at 10 frames per second, TEN frames. Critically acclaimed, reviewers loved it and didnt tend to mention TEN frames per second on base consoles, not pulled from the store.
If this is a serious question, I'd say cut any of the new vehicles introduced in the last 2 years. None of them are nearly as impactful as this optimization. In fact, I am having issues imagine any individual feature at all that's as important as this fix.
Unfortunately this part often kills quality initiatives. Why fix bugs for your existing customers when you can deploy the engineering resources on a DLC or a sequel which will milk those customers for more? There is no more craftsmanship or pride in good work left in software.
"When you're a carpenter making a beautiful chest of drawers, you're not going to use a piece of plywood on the back, even though it faces the wall and nobody will see it. You'll know it's there, so you're going to use a beautiful piece of wood on the back. For you to sleep well at night, the aesthetic, the quality, has to be carried all the way through." -Steve Jobs
This is what you'd need to decide. And then afterwards, it might not print as much money as you think it will.
It's easy looking at it from the outside. Not so easy from the inside.