Please, stop that "tons of graphical features" thing. Taking apart PR sentences, what screenshots showed is lower polycount in definitive edition. No more. Tessellation on pc adds a ton of polygons in characters, world and objects. A ton. LOD settings are lowered in trees if we rely on released screenshots. We have yet to see the quality of ambient occlusion. In the PC version there is no ambient occlusion switch on / off, there are several levels of quality, as with the shadows. The first TressFX in game release had a big impact in performance. After TressFX patch, they improved physics precision and performance a lot. Definitive edition will have a new version of TressFX. Multithreaded renderer only can be enabled on PC version modifying a registry key (because they don't do a wide phase of testing), and produces a big gain in raw performance. That option is enabled by default in definitve edition.
Basically, if you could set the quality options in your pc as definitive edition, you would have a MUCH better performance than setting options at ultra.
Changes that will be more visible for console gamers are all artistic changes and not affect performance.
They spend that time porting the game, and in that time, most of them are working in the new Tomb Raider, they used few of next TR assets on that Definitve Edition (face, skin shader, new particle system). Surely they don't create those assets for that version.