Yes, that's right. It seems inappropriate to say that workers are slaves. Because slaves with work are also very different in meaning if our slaves are forced to work even without being paid. If the mindset is like that, I'm afraid all employees will feel like slaves to the company.
Even though we all know that without employees, all companies cannot run. Without civil servants, all governments cannot run, so it is not appropriate to say that work is a slave. Because basically the financial system and media including social media ultimately direct today's humans to have to live like that and they are consciously willing to compete until humans run out of time, they are also fully aware. But I think that's normal because everything still has its benefits, and that's how the world works.
Although those words are not quite right, if we examine further, there is nothing wrong with what the OP said that in certain companies many employees are treated like slaves without any progress in their lives to be able to advance further.
It is true as you said that employees are the main pillars for the progress of a company, but we must also realize that most employees do not have career development even though they have dedicated many contributions to a company.
It all depends on the settings and the can of job we are doing. There are some jobs that will take the strength out of you without living you with something to save for the future. These kind of jobs can be very tasking and does not give us time to relax and think.abiut ourselves. Professional jobs are different because they are flexible and with lots of time to spend on vacation with allowance to take care of some bills. This also depends on country and the sector of the job. In advanced countries, professional jobs are the best and can take care of some many needs having something to save.