Sections will continue to be maintained so no fear that it won’t work or won’t be supported in the future. The one function missing from Gutenberg without additional plugins is the ability to create Sections / Rows. If this is not a requirement then yes Gutenberg would be a good direction to head in. If it is a key requirement then i would stick with Sections where required for the time being.
There is of course nothing stopping you from using Sections on one page ( where rows are required ) and using Gutenberg on pages and posts where they are not.
SEO wise – there is no difference.