I think the whole problem with systemd wasn't just about technology. The results were spectacular. Before systemd normal Linux boot times were well over a minute. After switching you could get below 10 seconds on the same hardware. And that is just one aspect.
I think the core of the problem was somewhere between the style of introducing changes and the way how people communicated. After all, it speaks for itself that pulseaudio and systemd shared a lot of common criticism. Both are technically sound systems today, but in a way, systemd was just the escalation of the pulseaudio debacle.
SystemV init allows for init scripts to run in parallel, but that was rarely used. Most time spent was anyhow waiting for network (e.g. the MTA trying to resolve the hostname) and hardware initialization. Bourne shell isn't particularly fast, but ten years ago hardware used for typical Linux desktop/server systems was fast enough that it hardly mattered (it's used here for sequentially starting system processes, not number crunching). Not that it matters -- how often do you boot a desktop/server in a day? Performance mattered for VMs deployed in the cloud on request, but whether a full OS is the best choice for such services is a different topic ...
