You aren't giving anyone an advantage by letting them mine on your blocks because it's either your blocks or someone elses blocks they're going to be mining on.
Certainly they gain something. By building upon your block rather than beside it the probability of their next block becoming an orphan is reduced.
Question: What does this obscure example of a network with terrible rules have to do with anything?
I don't know about you but I'm talking about Bitcoin with it's current rules.
If there are 10 blocks per second they could easily be mining on someone elses block. They benefit you by mining on it.
You aren't talking about Bitcoins rules. If we were talking about bitcoins rules we would be talking about blocks that are propogated in 1/500th of the block generation time, not 10 times the block time.
