I know some companies have solved this type of problem by computing some "seniority number" based e.g. on date of graduation / years of experience. So person A and B graduating at the same time -> A goes to work for FooCo, B works somewhere else for N years, then joins FooCo, both get the same salary for the same position. I.e. quitting and re-joining does nothing.

Then the mechanism for rewarding high performers is to give them a better position (e.g. Engineer -> Senior Engineer -> Chief Engineer) instead of just raising their salary with the same title.