Canvas (and Claude Artifacts) aren't things you use inside a large codebase, they're more for one-off tools that you may want to run, without the hassle of setting up a stack for each, copying code between the LLM and your local editor etc.

Think "here's a schema for some internal API, write me a tool that lets me put in a product ID and see the number of purchases, chargebacks and returns for that product over time, on graphs, also provide sortable by-country tables for these stats".

With artifacts, software goes from something you make once and use for a long time, to something you make at need, to do exactly what you need and no more, and then immediately throw away once it has served its purpose.