Limiting computational power can also filter non mining nodes. Is there a problem?
Yes, because then only miners will be able to verify data. If you ban all nodes that are not mining, then you will have only miners in the network, and then the whole P2P concept is gone, because all other users will then be entirely banned, and would need to connect to the network by using some miner as a proxy.
Suppose I created a fake coin using Bitcoin running code, but I added two restrictions to this fake coin. Each user can only have one account, and the computing power of each account is limited to 100M. This fake coin has 1000 users. If someone tries to attack with 1T computing power, is the network still safe?