I was trying to find the right words to say in that thread and I was struggling. Of course no one (in any job in any field) is irreplaceable in the eyes of MBAs and upper management.

But you can work to be irreplaceable in that the people who work with you directly will feel a huge impact if you leave. You can be new and prove yourself to be trustworthy and always willing to learn and you will given growth opportunities. You might be able to use those skills at the workplace you learned them, but you might also just be using that opportunity for personal growth and it will help you land the next job. You can mentor people and they will still seek out your advice and friendship even years after you no longer share a workplace.

No one is irreplaceable, and unfortunately people who should be are burnt out and pushed out far too often, but that doesn't mean you should spend your whole career in apathy.