It can also be disappointing to go through a multi-week onboarding full of outings and lunches and fun activities, only to discover that the real job is nothing like the onboarding. Then you have to learn how to actually do the job after the onboarding.
IMO, the best onboarding strategies give the current employees and the new hire some room to get to know each other naturally, without forcing it into overly structured activities. For example, giving the whole team a budget to go out to a long lunch with the hire 3 days per week on the first 2 weeks.
Unless you have a team of lone-wolf type or antisocial developers, usually the person's peers have a better idea of how to onboard a person than a manager several steps removed. Or worse, a person in HR trying to imagine what a good onboarding activity looks like for engineers.