If that's what you want, why in God's name are you wasting time with the blockchain?
You could get all of what you want, for 0.1% of the CPU and memory cost, using a boring old 1970s vintage cryptographically signed ledger. (The Merkle tree was patented in 1979.)
As for the "mainframe" story, well, the whole Ethereum world computer, which has 300,000 nodes, has 1/5000 the computing power of a Raspberry Pi 4. Eight orders of magnitude of inefficiency isn't something you can just wave off!