The distinction between the two though is projects and coding tests are work actually potentially useful to the company, things they could take and use where what you're talking about isn't part of the normal work of an employee.
You underestimate the insight that comes with looking at different solutions to the same problem.
I have been showing the value of GraphQL to a few startups for a while now to the point where I can get a GraphQL/Express server up and running from a frequently used template I built, in 90 minutes will full support for Query, Mutation and Subscription.
Create new users, tasks, updates, votes? Check
Check Update users, tasks, updates, votes? Check
Get realtime notification of changes to users, tasks, updates, votes? Check
This new insight has tremendous value to a company that's struggling with a RPC like system hidden behind "REST" endpoints.
At a company I know the R&D team routinely interviews PhD candidates of which an hour is kept aside specifically for the R&D team to come up to speed on the latest research that these PhD candidates read up on.
> The company is spending time and money (a LOT of money at big companies) to interview you, expect to spend some of your own.
I dont think you thought this through.
The company is spending time and money to make sure they don't make a hiring mistake. The time and effort sunk in by the candidate is part of the cost subsidized by the candidate.
An argument can be made that it would be cheaper for the employer to hire a candidate on an at-will basis once the candidate passes a basic skill and design test.