To improve the mod compatibility this mod has with other modded biomes, I feel minecraft:is_end should be used. This is found in 1.21.1 NeoForge

https://github.com/misode/mcmeta/blob/b7e7f5282f9cc2ca1bd01e9a4911beab4725cb4b/data/minecraft/tags/worldgen/biome/is_end.json

However, you would need to create and register a new class that extends RandomSpreadStructurePlacement and override isPlacementChunk to not spawn within 1000 blocks of world origin to prevent spawning on the Ender Dragon island. Definitely doable and worth it to get compat with all End Biomes.

https://github.com/TelepathicGrunt/RepurposedStructures/blob/11e6b0bd15d0fe1d9a990a231511ecaf09ee35c7/common/src/main/resources/data/repurposed_structures/worldgen/structure_set/pyramids_end.json#L13

https://github.com/TelepathicGrunt/RepurposedStructures/blob/1.21-Arch/common/src/main/java/com/telepathicgrunt/repurposedstructures/world/structures/placements/AdvancedRandomSpread.java

Furthermore, you can have a custom structure class that check if the land at the spot is higher enough to allow spawning. This will let your mod avoid spawning in no-land modded end biomes

https://github.com/TelepathicGrunt/StructureTutorialMod/blob/211c5cdfb2e97a3a111df8aaba7697d409c38316/src/main/java/com/telepathicgrunt/structuretutorial/structures/SkyStructures.java#L103