Working as intentional. Leather armor only slows the freezes process, it doesn't stop it.
This isn't the place for feature requests. This is a BUG TRACKER. Please head over to the feature requests page -> https://feedback.minecraft.net/hc/en-us
Also, Mojang have already stated that they won't be adding dynamic lighting anytime soon.
Amethyst Geodes aren't structures, so I don't think this relates to that
This will be awful for combat... I thought you guys learn your lesson form 1.9
Done, added screenshots - the same resource pack is active in both. Left is 19w45b, right is 1.14.4. You can tell the pack is active by the transparent hotbar
Can confirm for MC 1.14, 1.14 Pre-Release 1, and 1.14 Pre-Release 2. Can't spawn the Wither, and no mobs spawn in the overworld. NONE.
This bug only happens with there are no structures in the "structures" field. I closed this issue because I figured that out.