And with an x3 lower average fee which you successfully managed to omit from the equation.

With 10MB blocks, costs of running a node would increase exponentially.

signature validation (which is currently still the majority of the CPU cost) scales linearly with the number of hashes. Signature hash computation scales O(num_transactions * avg_transaction_size^2). Database lookups/updates scale O(inputs) and O(outputs), and each will get slower over time as the UTXO set grows.