In my opinion, the 100 reports limit is quite good, the reason to why I think that is because based on only a few reports, it's hard to overview the player.
With previous experience, it's important to really make sure that the player who is being considered as staff know how to properly report a rulebreaker ect, with 100 accepted reports, it's a bit more to look at and judge from. If they lower the limit, they might accept someone who isn't too familiar with most of the rules and might make a few mistakes later when they either report as a Helper or punish when they get promoted to Moderator.
I know that being a Helper is like a trial, you learn how to deal with things ect and we all ofc make mistakes, but it's quite hard to know what exactly you need to teach your new staff member if you haven't seen much of their work and don't know how much they know about the role.
Making reports is also considered as putting effort into the server. It's a way to see how much a player care for the community and how well they would fit for the role. So it many ways, it's important when you overview the player in general.
On a sidenote: Yes, it is possible to overview a player in other ways but if the player isn't super active on the forums ect, and doesn't talk much, reports can be a way for them to get accepted anyway.
