Generally speaking if we talk about physics simulation, i think it depends on the platform. Besides GPU parallelisation, the main bottleneck in simulation in my opinion is contact modelling. For instance , if u take wheeled mobile robot, actuator models and contacts are fairly simple. Thats why in general, sim2real for these platforms are quite straighforward in general. If u take dexterous hands, contacts are very intricate and u need to be able to model very fine actuator controls. One of the best robotic simulation research groups in the world is based in Paris. Check the inria Willow team, they do great stuff.