Resigned a few days ago for the same reasons. I have been working no less than a senior for months, and each month my company made me remember that I am a junior.
Well, I am not counting the time/energy I spent for the job, but I am comparing the outcome of my work. I agree that I sometimes work a little bit more (by means of time) than a senior engineer, but as the outcome of my work matches the senior, then I want my salary to match or come close to seniors. Definition of senior here is "someone who works for 2 years in development." Nobody cares if you suck or excel in your job during the 2 years.
If anything, I expect junior developers to work a bit more than senior developers to accelerate their learning.