rsync is not the same type of backup, so please don’t think that by using rsync you’ll have the same level of backup as you would with restic.
Regarding installing spezialized software, restic is one single binary. It’s literally just a file you download, so that’s not much of “install and configure specialized software”. Also, if you already didn’t want to install anything beyond what comes with macOS, why did you even open this thread in the first place? I don’t really understand what your actual question is.
Here’s a summary:
Use TM if you want super easy to use but don’t need the same level of integrity and safety in your backups, and beware that TM does not always work great (I personally stopped using it because it was too buggy). Requires nothing extra to browse the backup storage.
Use rsync if you are happy to configure the rsync command a bit (not for those that want the simplicity of TM, and it’s arguably more complex than using restic), and want just plain “file copying” type of backup. Requires nothing extra to browse the backup storage.
Use restic if you want a backup that you can verify the integrity of and might want to protect with a password (even if you don’t want to do that, you can just use a simple password and it’s not an issue that it is password protected). Requires a single binary and FUSE to browse the backup storage (but requires just the single binary to list and restore files).
In the end I think it’s a matter of what type of backup you want. Do you want one that will cover your ass and be able to let you know when you have bit rot on your disks, of do you want one that just copies your files for you