My understanding is that for SEO purposes, CTR and other bits and bobs it’s better to have this.
The only method I can think of, is by creating single pages, which defeats the idea of a CMS.
I’m sorry but no you can’t change the url structure of collection template pages.
About SEO, actually it’s wrong.
If you want an efficient seo, google needs to understand easily the structure of your website and locate where are the articles, where is the homepage etc.
If you want to improve your seo and get the most of your juice on the homepage you should consider this kind of structure : (edit : link in absolute is better)
Which is not the very best for a user experience (because it means people need to go back to homepage to access to the complete menu) but it’s definitely the best for seo.
You can’t eliminate the /slug/ and still use the CMS. (You’d have to create individual pages to do that - not optimal!)
But you can be creative with the slug by using silo architecture, which actually helps your site performance. You can use a /theme/ or a type of /user/ or the like.