"tools-used" was added because Ackis was including data-tools as an embedded library in ARL so that data-tools would get reward points since he heavily used it. It is the exact same thing as an embedded library as far as points go but it does not cause the nolib mode of the Curse Client to try and install a standalone, which is the problem Ackis caused.
Hard embedding should never be done because external code not under the control of the addon author should not be in the addons repo. This is even worse for LDB because LDB does not have any copyright notice anywhere so every addon that is hard embedding LDB without adding an exception for it to its own license information is technically violating copyright. I'm sure Tekkub doesn't want LDB under GPL but a GPL addon hard embedding it with an exception being listed is technically illegally declaring that it is under the GPL. The same could be said for addons that reference it as an external too but in that case the repo does show evidence that the file comes from somewhere else.
The "license-output: LICENSE.txt" .pkgmeta feature of the repos should probably be changed to give the license of the addon and all embedded libraries automatically when used, but that still wouldn't even help in a hard-embedded situation.
If Tekkub does not want there to be a standalone version of LDB then he should tell authors to disable nolib zips for their addons using "enable-nolib-creation: no" not by encouraging hard embedding of the library.
I support the idea of allowing libraries to be specified as not having standalone versions and always being included in nolib zips because of LibStub and CallbackHandler, but since I have been fighting for that since WoWAce moved to the CurseForge system and there has been no sign of anybody with the power to make that change supporting the idea so I see it as a lost cause.
If somebody is only using LibStub, CBH, and LDB in their addon then they should just disable nolibs instead of hard-embedding. LibStub and CBH should never be hard-embedded on WoWAce/CurseForge repos (but there are still a lot of old libraries that do and should be fixed if they weren't mostly dead).