How is Canva any different than this? Part of design is being able to recognize what good design is, and utilizing the tools available to you. If Canva get the job done, and looks good, and has been sufficiently modified to meet the specified criteria supplied in the assignment or spec, how is it cheating?
The only way I could see is if they didn't modify the slides and part of the assignment was to create a unique branded slide presentation and they just used an out of the box design. In which case, no design work was done.
Someone shouldn't be penalized for the outcome based on the tools utilized unless the spec specifically excludes it.
It's like telling a clothing e-commerce company that they shouldn't use Shopify. If the work is done, why waste your time building an e-commerce site from scratch if it meets the specified need?
Canva is a great tool, and saves my clients thousands of dollars, while I get to avoid doing the completely mind numbing process of working in PowerPoint or designing social media posts. It's a win/win.