Ethereum project has become a victime of Ddos attack, slowing down the transactions and giving priviliges to attackers to mine blocks. So instead correcting bugs in geth or parity is there any robust solution (increase opcode cost, or hardfork)?
A hard fork is necessary to improve the pricing of the opcodes.
Here you will find an explanation from Vitalik about the EIP150 Wherein he rebalances gas costs to resolve remaining DoS issues. Recently gavin wood has called for a hardfork to fix the problem. He said:
“We need to revise our gas costs, surely. Doing it quickly isn’t an option.”
but I think the community is still skeptic against the word "hardfork", because the last time it leads to a split in the community. This hardfork is different so no worry for a Community split.