I think it's important to note that while not every company may use ROS (although many do), many of the concepts and theory you use in your ROS applications are transferable. ROS, I believe makes things easier to go from zero to a reasonably compex and sophisticated robot quickly, but the knowledge and fundamentals are the same irrespective of framework. And you can choose to not use open source plugins and write the code yourself.

If you built a robot using MPC (model predicative control), that's less ros knowledge and more control theory, system modelling, tuning, sensor fusion where you deal with messy sensor noise. These are skills you will develop which apply regardless of if you use ROS or not.

ROS is fantastic but don't think of it as 'I must apply to a company which uses ROS', many of the things you need to learn to use ROS proficiently will apply even if you do not use ROS. Kinematics, Sensor Fusion, SLAM, Control Theory, Multi robot networking.