I think that the main issue is that there is not much information about those system indices, what they are used for and if they can be removed without any risk of breaking something.
I made a similar question a couple of months ago about the slm-history and ilm-history, but got no answer.
One of most repeated recomendations from Elastic is to avoid to have lot of small indices and yet Elasticsearch itself keeps creating those small indices without any explanation if it is safe to remove or not.
It would be nice to have some information in the documentation of what is safe to remove or not depending on which features you use.