Why in the hell is
https://mods.factorio.com/mod/freeplay_starting_equipment
marked as a necessary dependency to use this library?

It does nothing related to the library. It's just a starting items mod.

PLEASE remove it from the required dependencies.
It's ruining my attempts to use a hardcore start mod with your mods.

Hi.
The game starts with burning generator and some stuff. The early versions have built-in code to add the stuff. After some version it was moved to standalone part.
You can still edit starting equipment for you hardcore start with any setup with settings (3 option is available to tune your experience).
If you have some bugs or errors - pls send logs/save/screenshots.

Mod settings->Map->Adjustable freeplay starting equipments->...
- Use defined starting items with any other mods [can be unchecked]
- Ignore any overrides by other mod via mod remote API [if you want fully custom set of starting item better to set checked]
- Stating items [your own list for your hardcore run]

If you've used the apm lib w\o apm_power & other apm's mod - hmm. Provide usage scenario. In current code state assume using the "hell" mod.

While there is no any actual information - the topic will be changed to "custom startup items options".