It's puzzling why the studio couldn't do this. The problem itself is easy to spot by a performance engineer, and avoided in the first place by an experienced developer. Did all the leads leave after implementing the prototype? Did management fire the whole team after the release? Were sales good enough that nobody really cared?
The issue was the original studio didn’t stipulate good enough performance targets or were already over-committed to this contractor for the timeframe.
Getting 3D working optimally so that it uses the hardware maximally is actually hard. There are lots of places where you can use the wrong call and something ends up being shunted to the CPU instead of the GPU and all your performance is gone.
As a dev you probably have a really fucking fancy machine on your desktop which hides all the sins you are coding into the game.
Studios sometimes just want bodies and hire way too many inexperienced devs who haven't been through all the gotchas.
Also, you need a good profiler, you need to know how to understand your profiler and you need to profile often on a game to make sure you don't get to the end and find some horrible bug that requires you to go back and ask the artists to change all their assets.
from my experience, toy-makers don't use military-spec parts