You are misunderstanding what this solves. Believe me, if some easy solution would have existed, it would be there already. Essentially a fork before such checkpoints would destroy the network. Although the probability is low, this is a very non-trivial effect. Checkpoints eliminate the possibility. Yes, the pure algorithm in the paper and reality can diverge rather strongly. The downsides of this approach are in a way trivial, as long as enough people ensure the codebase is not corrupted. Centralization is a problem, but it is not at all binary. And yes, Bitcoin as an ecosystem is much more central than one could hope for. But there are very good reasons for that, and changing this is an extremely hard problem.