[ALL THEMES] Theme Uses Many Image Sizes And Plugins
1. Using multiple sizes of picture gives the site the ability to work on mobile devices better. It’s the same for any responsive site, and yes, it is inevitable disadvantage.
2. Again, using plugins is a downfall of a CMS. Also, it is a practice of ThemeForest’s requirements that a single plugin should do only one job. Please choose the one that you only need.
To improve performance, please check this FAQ: https://cactusthemes.com/knowledgebase/themes-website-slow-can/