If you want your Discourse instance clear of independent theme components that’s responsible for adding custom css for a particular plugin, you could perhaps instead create a single theme-component that’s responsible for all your unique customizations you want for the plugins you have installed.
Inside that theme component, you can then split up all your files into multiple .scss files and import them in a main common.scss
my-theme-component/
├── about.json
├── common/
│ ├── common.scss
│ └── head_tag.html
├── scss/
│ ├── announcement-bar.scss
│ ├── banner-featured-links.scss
│ ├── category-banners.scss
│ ├── disco-toc.scss
│ ├── topic-list-excerpts.scss
│ ├── topic-list-thumbnails.scss
│ └── disco-toc.scss
└── settings.yml