Speaking as someone who uses OpenRC on all my machines . . . no, systemd is not necessarily slow, and personally I don’t care about the speed of my init system anyway. Thing is, systemd also has nothing that makes it more useful to me than OpenRC, so I have no incentive to change. Plus, I dislike the philosophy behind it, the bloat, and the obnoxious behaviour the project showed when interacting with others in its early days. I’m a splitter, not a lumper, and systemd’s attempts to absorb All The Things strike me as rather . . . Windows-like.
So, in a technical sense I have no reason to believe that systemd is inferior to OpenRC + sysv, and it may be superior for some use cases which are not mine. I don’t spend a lot of time ranting about it, and I see no point in trying to convince people not to use it if it fits their needs. But I still won’t use it if I have another option.