It's good advice sure. But downgrading their work, no. Unless you have explicit requirements that aren't met like your text being selectable, downgrading work because you have a prejudice against an authoring tool isn't cool. What if another educator has an issue with Power Point, and another with Sheets. Should students have to match their authoring tool with their educators for each lesson?
Students are there to learn, no to cater to your preferences.
What you're saying makes sense... if the OP explicitly tells the students to make their work available in a shareable and copyable format. The vast majority of presentations in schools don't live beyond the moment the presentation is finished.
Students are there to learn, no to cater to your preferences.