It was today that I found out that the standard AI has no impact on the behaviour of the bot_weapons setting.
That is baked into CS2D.

Therefore, I must ask, does the same apply to bot_skill?
Because in the built in standard AI for the bots, there's only one check for the skill setting, and that is if the bot should buy armour on spawn or not.
That seems odd, so is there internal logic handling bot skills or is bot skills just simply not used very much (only once) by default?

Bot skills are used internally. They affect these things:

what you already found out: if bots buy kevlar(+helmet).

perception range: how close do enemies have to be to be so bots aim at them. This is only a difference of like 30 pixels between worst and best skill so it's doesn't have a huge impact in most scenarios.

max rotation speed: This affects how good/fast bots are at aiming. Probably has the biggest impact on difficulty!

Are the last two things not modifiable by the Lua bots folder?
This is what I mean by "baked in".

Yes, these skill effects are hard coded and can't be changed with Lua.

The only way to work around this would be not using the built-in methods ai_findtarget (to get rid of the perception range skill impact) and ai_aim (to get rid of the rotation speed skill impact). Instead you would have to find targets manually and also rotate bots manually using ai_rotate.

Probably replacing ai_findtarget is not worth it because it will (probably) be much slower using pure Lua and also, as I already said, the impact of the skill isn't huge there.

Replacing ai_aim with your own rotation logic shouldn't be super difficult though and probably also shouldn't affect performance that much.

Thank you for the vast amount of knowledge.
I don't seek to change any of that, rather I only seek to understand it for I'm making a bot A.I. from nearly scratch and I needed this cleared up so I'll know what I'm going up against.

Thanks again.

You're welcome. I improved the documentation for the related commands a bit so things are more clear.

You might want to document the "hooks" for bots as well.
Although they're not added, and are documented in the default folder, having them on the website too couldn't harm.