Sluggish behavior in custom input type

[tinykite]

I'm currently working with an input type that allows an author to upload multiple images for embedded image grids within the blockContent of a blog post:

export default {
  name: 'imageGrid',
  type: 'object',
  title: 'Image Grid',
  fields: [
    {
      name: 'images',
      type: 'array',
      title: 'Images',
      of: [
        {
          name: 'image',
          type: 'image',
          title: 'Image',
          options: {
            hotspot: false,
          },
          fields: [
            {
              name: 'alt',
              type: 'string',
              title: 'Alternative text',
            },
          ],
        },
      ],
    },
    {
      name: 'display',
      type: 'string',
      title: 'Display as',
      description: 'How should we display these images?',
      options: {
        list: [
          {title: 'Square Grid', value: 'square'},
          {title: 'Mixed Grid', value: 'mixed'},
        ],
      },
    },
  ],
}

Adding this as a fieldtype to the BlockContent schema file seemed to work, but I noticed that — while working locally — the Studio UI seems to get very sluggish (a few seconds delay inbetween keystrokes) when editing the alt text field for an image, for example:

What seems to coincide with this is that the post appears to also save on every keystroke, rather than after hitting a "done" button. Confusingly, the performance is additionally much better in the mainblockContent for the post.

Is there anything I can do to further debug this behavior, or improve the performance of Studio?

Somewhat tangentially, I noticed that on its own the image input type does not appear to allow authors to specify alt text for an image. Am I understanding that correctly?