Does anyone know of any mods for 1.14 that let you stop certain mods from ever spawning?
There might be but I'm not too sure of any off the top of my head. The many I know are for 1.12.2 and prior like In Control or Custom Mob Spawning.
If there is any I have posted in this thread that I update daily with mod posts for Fabric and Forge 1.14 mods then you might find a mod that may do what your after:
'Niche Community Content Finder' for fun and support of creators. I look for mods that interest me or need a bit of acknowledgement or bug fix testing/reporting. I also make modpacks/maps
Creator/Maintainer of Fabric, Rift & Tesla Mod Discussion Threads/Niche Mod Youtuber.
1.15 Fabric: https://www.minecraftforum.net/forums/mapping-and-modding-java-edition/minecraft-mods/mods-discussion/2988502-fabric-1-15-snapshot-discussion-thread-install
1.14 Fabric/Forge: https://www.minecraftforum.net/forums/mapping-and-modding-java-edition/minecraft-mods/mods-discussion/2938388-fabric-1-14-mod-loader-mod-discussion-section
1.13 Rift/Forge: https://www.minecraftforum.net/forums/mapping-and-modding-java-edition/minecraft-mods/mods-discussion/2925529-rift-1-13-mods-discussion-section