How Effective Is Changing the PoW Algorithm as a Long-Term Defense Strategy?

Changing the PoW algorithm (a hard fork) can be highly effective in the short term, especially against ASIC-based attacks, as it immediately invalidates the specialized hardware used by the attacker. However, it is a costly and disruptive process.

In the long term, new specialized hardware for the new algorithm may be developed, or the coin might switch to an algorithm with low hashrate diversity, making it vulnerable again. It is a temporary fix, not a permanent solution.