Of course HR is the company rep, and sometimes one who is happy to forget things which aren't in writing. If you want someone advising your interests, pay a law

Of course HR is the company rep, and sometimes one who is happy to forget things which aren't in writing. If you want someone advising your interests, pay a lawyer. Engaging with HR is still a good idea. Ensuring a fair and reasonable process for evaluations and promotions and bonuses is very much in HR's domain. When there are problems of the sort OP talks about, HR should at least be aware of it.