Exactly: large files, ugly slides (I teach design) and impossible to select text.

The template driven nature on Canva also makes it really hard for them to learn multi page layouts and structured documentation.

The one thing in its favour is that it supports collaboration.

In Canva we do care about accessibility. While I admit our editor may still have a long way to go on providing an accessible editing experience, unselectable text in export result is more likely an overlooked bug than anything intentional.