These static numbers make no sense to me, higher level PCs that focus on this stuff will pretty much always succeed unless there's some other rule they haven't revealed yet. I think it's the wrong direction to take the game.
Static difficulties never work for any system for long. It's the biggest problem with for example the BRP system used in CoC is that it doesn't really provide good granularity for things being more difficult than usual. Rules in 7e try to codify and solve the problem, but even then there are issues.