I suppose it's tempting to make it a server-level setting alongside min/max server memory, but I'm not sure if I'd want this one to be so accessible. This could be a pretty powerful footgun. It seems like a more specialized configuration change that I'd expect someone to make alongside something like MAX_MEMORY_GRANT_PERCENT.
But yes, if someone is hitting RESOURCE_SEMAPHORE, and you drop MAX_MEMORY_GRANT_PERCENT down to 10%, you will generally increase concurrency and allow more queries to run, ask for smaller grants, but still end up hitting the ~75% total.
Instead of three queries running and getting ~25% a piece, you end up with 8-10 queries running simultaneously with the lower grants. RESOURCE_SEMAPHORE is gone, but so is most of your buffer pool (assuming the grants are fully utilized).