All the problems, concerns, advice, and feedback on challenges, other workers, etc. that you gave while you were an employee should have fixed any of the items which you communicated about. If they did not listen when you worked there, or if you were not forthright at that time, what makes you think they will listen after you leave?
A previous employer of mine had a project manager which had problems with their projects with every tech which they used on their projects for 3 years. This PM had about 8 techs that had no history of issues on their previous projects, but only came highly recomended by their clients. Every tech reported the PM's lack of skill, and commitment, but no action was taken. The PM was good at playing the game, and throwing others under the bus, including throwing her operations manager under the bus to the techs to blame things on him. If management has not the due diligence to keep track of things, reporting issues to them simply makes you seem like a boat rocker in most situations.
You can tell a manager who does not want to hear anything, nor do anything about anything, and sees communication of issues as being a complainer. They say something like this.
" I do not want to hear about any problems, or complaints unless you have a solution to the problem"
TRANSLATION
" I AM NOT HERE TO DO MY JOB AS A MANAGER, AND DON'T YOU TRY TO MAKE ME. IF YOU HAVE A PROBLEM, DO ALL YOUR OWN WORK ON TIME, ON BUDGET, AND WITHOUT MY HELP, THEN ON YOUR OWN TIME NOT COMPANY TIME DO MY JOB, AND THEN GIVE ME CREDIT."
If they really cared they would be doing things to fix things without having to have you tell them what it is their job to figure out in the first place.