If your view is that blockchain data is not important, then I believe that you'll probably disagree with everything that I say.
No reasonable person would suggest such thing, blockchain data not being important 
A blockchain is a data structure that preserves data, a database. Any database goes through events/transactions continuously and as a consequence their state is subject to change through time. What matters from the perspective of most applications is the state and not the events/transactions. They are valuable as far as they are relevant as a part of the state. In Bitcoin case, a transaction is not relevant anymore when all of its outputs are spent.
Synchronization and consensus is not only achievable by the naive "rewind" approach like it is done in the current Bitcoin implementation, there are more robust, trust-less, and secure approaches as well.