The only way you can accurately evaluate and attribute the work of this hypothetical intern is to answer the question "what would happen if they took their idea and implemented it independently?"

* Does it require a big capital investment? the company provides that.

* Is it risky? The company gets a risk premium.

* Does it need a bunch of specialized resources? the company needs to provide those.

* More subtly, is it net-new or incremental value? Providing a company with something that boosts what they already do isn't evaluated on the incremental increase because you can't realize them without the previous baseline.

There are countless factors measuring value-add, making it extremely hard to allocate back to a single cog in the machine - unless you're a startup with very few cogs, hence they're responsible for all value (or costs).

If you want to be evaluated based solely on your individual contribution, put yourself into a situation where this is possible, i.e. do it all yourself. Otherwise join the broader team and take the benefits and costs that comes with that.