But as you pointed there is a display somewhere, even sometime a disk write …
Sure the batch by itself could be started from the command line processor or another batch processor, but all the operations usually get engaged in separate threads or processes running in background.
If my 40++ years of programming in many areas clients/servers/clouds etc. skills have been correctly occupied building various apps with some still running.
TDLR, what kind of music are you doing with 700 tracks ? I’m not sure your Ryzen 5 3600 could handle it if there was audio and MIDI going on on each track, plus hundreds of instruments and effects loaded.
You say the CPU meter stays low when doing your experiment on empty tracks, simply because those plugins are automatically bypassed internally when they don’t receive any signal.
Try putting some audio on all your 700 tracks and hit play. All the plugins will turn on at the same time and your CPU will probably max out instantly, and not to mention that playing the audio alone takes CPU ressources too, it isn’t just the plugins.
Professional orchestral composers have machines with dual Xeon CPUs and more than 512 GB of RAM, and that alone can cost more than $10.000, this is very far from your average computer.
My PC has only 32 GB of RAM and I can barely load a few dozens of techniques from BBCSO, so 64 GB will clearly not skyrocket your max track count either, especially when a single multi-mic patch can easily take more than 3 GB of RAM.
Also, you may think that loading hundreds of plugins takes a lot of time (several minutes), but loading large orchestral templates/projects can actually range from 10 minutes up to more than 1 hour depending on the project size and SSD type (SATA or NVMe).
It doesn’t have to apply to this case, but sometimes a program is just slow. No matter how fast the computer is.
My favorite example is Sceanarist BD/UHD: If you load a big project there, it always takes a few minutes. No matter how fast the computer is. The same is true when you reassign orphaned files in Scenarist. This takes forever. (Even if this task would be done with a supercomputer. 
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