[Anything and everything AnnoyMint says]
This is just another in a very long string of attempts to find the "fatal flaw" in Bitcoin.
I already found it.
Now to recap, not only is a > 50% attack very destructive as I've successfully argued and defended above, but don't forget that my first point was also that Bitcoin will be relatively easy to 50% attack once the coin rewards decline, because there is a problem with transaction fees:
Mining funding will be miniscule after coin rewards end, because there is a tension with transaction fees that has no solution. If you scale tx fees as a percentage then they will become orders-of-magnitude higher than debit cards (apparently some have a flat fee), because of the very high value of BTC in fiat. Whereas, if you don't, then mining is underfunded relative to the value of Bitcoin's economy, thus a 50 - 95% attack is very likely. The only solution is to eliminate transaction fees entirely and keep coin rewards.
The stats are here, it's 0.69% of miner revenue (good guess!).
...is just $18,000 a day...
So with Transaction fees in the ~$30,000 range it looks like the fees are roughly able to pay for electricity, a somewhat surprising result actually.
You missed the failure mode.
If miner revenue is to be only a tiny fraction of commerce, then 50+% attack is extremely likely.
Only perpetual coin rewards can secure the network adequately.
Otherwise transaction fees must be too high, and also significant revenue from transaction fees allows the
Transactions Withholding Attack.