In Add new comment, Fields and button needs space.

After fixing the issue.

Verified MR4, the space is added for the required area in the comment section. RTBC++

Did you know you can use utility classes to apply margin bottom?

e.g. mb-4 = margin-bottom: 15px;

So in this particular case you can also override the template.

In fact I believe there is already a theme suggestion override in the theme. So in this case you could create container__comment_comment_node_article_form__subject_wrapper.html.twig in your theme.

I agree the layout should be spaced, out. How that is done is the question? What I am not in favour off is creating lots of specific styling tweaks that someone will likely need to override in their own theme implementation.

If we can come up of way that handles this more generically that I would be more inclined to go with that solution.

Really this comes down to what the issue is. Unfortunately that has not been clearly defined here and there is no description of what the actual issue is.

Also where do you get 15px from? Is this just an arbitrary value that works for you?