>>A transaction is definitionally something that has been written to the blockchain, so no it isn't.
You can have a smart contract that writes reversible transactions to the blockchain. This would mean that the smart contract imposes a delay for withdrawals, to allow time for any possible requests for reversals. There could optionally be an expedited wirhdrawal upon some set of authorities deeming the balance as finalized and not subject to any reversals.
>>requires secondary solutions that violate the very core philosophy of the data structure in hopes of overcoming just one of its many issues.
Even when you lose some of the benefits of blockchains, via secondary solutions like a reversible transaction smart contract, you retain some benefits, like:
* optionality, e.g. those who are fine with irreversible transactions are free to use them,
* permissionless market entry, e.g. any party is free to deploy their own 'reversible transaction' smart contract, giving payment consumers maximum choice
* stronger guarantees of the integrity of transaction processing, with transparency into any tampering, given the code that executes the transactions, along with the transaction itself, is publicly auditible
* debundling the provision of the different services that are required for transaction processing, by allowing transactions to be processed by immutably open smart contracts that no third party can later close off access to.