Yes, it does affect the hashrate since miners stop mining once they reach the mining cap, but at this stage that doesn't have any negative impact. You need huge hashrate to secure the network when anyone is allowed to mine, in order to prevent a huge hashrate holder to highjack your blockchain and fork it as will. IoP in its current stage is not open for anyone to mine, so it doesn't rely on huge hashrate to keep the network secure. As time goes on and the chapter network is fully built, mining will be opened to anyone. But even anonymous miners wont be able to attack the network with hashrate at that stage either, since there will be by that time a PoS / PoW hybrid which will prevent a single entity to mine two blocks in a row, meaning that they can never mine outside and later produce a fort of several blocks.

In short, hashrate is only important in pure PoW blockchains. When other mechanisms are added they lose relevance, in some cases like ours, a lot.

You can learn more about the chapter network we are building here:

https://docs.google.com/document/d/1BOB3Xc5vHNKBNZJeosXGi0iNCxiD6rbFTvbF1uXfv10/edit#

And about our ideas of an hybrid PoS / PoW here:

https://docs.google.com/document/d/1fwXOCfX0zfJv-MloeVAsVjS_JEpfdIXHUObMBijLrJ8/edit#