I'm not sure what you mean corruption, journald logs should actually fare better in terms of dealing with corruption and tampering versus text logs, if you use the log sealing feature. You could also already easily plug any of the syslog implementations in.
Perhaps he is talking about modularity - systemd is a bit all or nothing, it is a pluggable system yes but (AFAIK) it is not modular so you can't write arbitrary software and have it adhere to some standard, instead you have to use the systemd libraries and link against systemd calls.
So it is another layer on top of the kernel in that sense.
The old alt was to put the shell in charge and bash or sh talked to a bunch of random programs. Which is in some ways more modular but also a bit of a nightmare...
I'm not certain anything like that exists, you would have to define some data architecture almost, maybe involve hardware like ACPI and UEFI...
But that goes back to nobody basing their career over how a computer boots...overly complex. Maybe better just to improve systemd instead.
