zaměstnání could be employment as well as job, couldn't it?
yes. Though employment is uncoutable
Employment is both uncountable and countable. Uncountable is used way more often in everyday conversation in the meaning of general employment, but countable does exist as a synonym to job, e.g. "List your previous employments."
Look for a better employment was suggested, but when I tried to use it, I got an error.
I'm not sure if it's correct or not, but it shouldn't be suggested if it's wrong.
Think of the “suggestions” more or less as of a dictionary. Not every translation for a single word is appropriate in every context.
If you think “employment” should be an accepted translation I suggest you ⚑Report it.