Short version: some people (I’m one of them) object to systemd on grounds that are 75% philosophical and 25% the kind of tech detail that’s more of a matter of taste than anything else. The older sysV init is a smaller program, which means that it has a smaller absolute number of bugs than systemd but also does less on its own. Some of us regard “does less” as a feature rather than a bug.
If systemd works for you and you don’t know or care about the philosophical side of the argument, there is probably no benefit for you in switching.