Different people have different definitions of complexity. For me having a single point of failure is complexity, for most people a centralized single process handling as much as possible is simplicity. Neither is right or wrong.
Whether a system is tightly coupled is independent of whether it's implemented as a single process. Objections to systemd as monolithic, as constituting a single point of failure, etc. are based on its being a tightly coupled set of components.
That systemd is tightly coupled is a valid objection, but "single process" has a specific meaning in this context and it implies a much worse design, with every component potentially taking down PID1. As far as I know, this is not the case in systemd.
