EGL is primarily about windowing system integration, it's what lets you initialize an OpenGL context in the first place.
It doesn't really accomplish interop between different APIs on its own, though of course various interop methods are based on it — e.g. if you want to import a dmabuf, you'd use EGL_EXT_image_dma_buf_import. But, say, on the Vulkan side you'd use VK_EXT_external_memory_dma_buf — there is no EGL with Vulkan, Vulkan has its own WSI subsystem.
It doesn't really accomplish interop between different APIs on its own, though of course various interop methods are based on it — e.g. if you want to import a dmabuf, you'd use EGL_EXT_image_dma_buf_import. But, say, on the Vulkan side you'd use VK_EXT_external_memory_dma_buf — there is no EGL with Vulkan, Vulkan has its own WSI subsystem.