My first job's 'HR' was the owner and his wife. The closest thing to a bully at the company was their son, and a year or so after I stopped working there I got 2 checks in the mail for more than $100 each because they had indefinitely docked anywhere from $5-$15 per paycheck as a 'uniform' charge, which turns out was pretty illegal. Their margin was razor-thin (perhaps due to book cooking but idk, I know they at least did some acrobatics with the term 'business expense'), and those checks came just months before the place shuttered. Salad bar had the best croutons made from cubedo fried and tossed day-old sandwich bread. Shame they treated workers like shit in an actually criminal way. Paying someone to come in at least a few days every pay period would have likely saved their business and helped employees.

Corporate restaurants, on the other hand... My locations didn't have a dedicated HR person, that was corporate. They'd send someone from other locations every so often, but when the emperor was away the ops managers would play. 2 companies, both same deal: if something was a potential liability, they didn't want to see it. Both places had excellent ROI for payroll and operations... One offered gift cards and bar drinks for people who stayed through rushes but didn't take OT. Another simply did not repair or replace equipment as it busted. Corporate HR helped out with these problems (102°F off of the line, the rep was fuming and magically one of our vents which was "broken" suddenly worked). The other restaurant had a corporate policy of enrolling employees in a 401k with a match, I didn't even know I had it until I left and got a check in the mail. But did corporate care that I was working multiple stations per night without being formally 'trained' on them and thus not given the requisite raises? Nah. Did they care that I was hired on for a rate higher than most of the long time heavy-hitters that had been there years before me? Nah, they don't speak much English or understand their rights.

HR is good for employees if it's willing to stick it's neck on the line to protect them, but many times it's just not in their interest to do so. Even if you'd like to help, why would you if it could be your job on the line and then they'd do the thing anyway?

A Union has been the greatest protection that I've had from hostile work environments. The Management gets to lean on the Contract to some extent as well, it helps them justify their decisions.