Yep those eth fees were crazy last year, but, that alone makes a good case for a free-to-use general purpose smart contracts chain.
I also doubt Hive would suffer another exchange attack, but, if it did, I suppose it would require a hard fork to mitigate within the 30 day window for witness voting. While that would work, having a mandatory hard fork as a feature isn't great. As we've seen before, PoS/DPoS works really well - until the day it doesn't. (not fear mongering, it'll probably all be just fine).
I haven't really followed EOS at all but I suppose that would be the next closest thing to koinos - as far as I understand it's split up into varying resources (cpu/ram/network) which isn't a great user experience and doesn't have payer/payee semantics like koinos or delegation like hive. It seems pertinent to be able to launch applications with free accounts and for dApps to be able to allow their users to use them completely for free in order for dApps to go mainstream.
The exchange attack wasn't enough, it was combined with the fact Justin Sun got 76M under the table without affecting the market. This will never happen again as no one party owns even close to that. I doubt exchanges will ever fall for that again I'm honestly surprised there hasn't been a legal action taken against them for their involvement and what they did to customers funds. Never too late I suppose.
Agree that the whole thing was a result of multiple factors. I also agree that Hive stake appears to be much more split up at this point. However, the protocol itself still isn't immune to these issues and stake can still changes hands. It's way less likely, but, not impossible over a longer period of time.
I'd argue it'd get harder over time, especially if the stake is distributed properly to people that value decentralization and wouldn't assist in such an attack, understand what went down the last time and how it hurt the people who helped centralize Steem, etc. Though currently with a somewhat high inflation and stake that's being sold being unaccounted for in who's hands it's landing on exchanges may be a risk. Either way even in the worst case scenario where the attacker were to slowly power up a lot of accounts with the stake they're buying to vote in their witnesses people would notice them going up the ranks, a lot of stake being withdrawn from exchanges going towards it, etc. Nothing a call to action to vote the witnesses they know wouldn't fix.