I think this all depends on individual birds. I have 14 birds. Some are very gentle, some are aggressive and will peck really hard. I have a bantam that becomes a lap pet if I have treats.
One of my young chickens is so gentle- when I offer a grape she daintily grabs tiny bits like a hummingbird sipping nectar. The others are like vipers striking out to try to grab the whole grape for themselves! It can smart a bit when they get ahold of your flesh, but I've yet to have one actually break the skin. Silly birds.