Fragility of Cryptocurrency

Does it scare anyone else that the backbone of the crypto-beast is bitcoin? 

There are a few forms of attacks against a network the most brutish and common is the DDoS attack where the network is flooded by traffic (usually from one malicious person or organization).

Currently bitcoin is acting as if it were under a DDoS attack because the network is at capacity. With more people (millions!) coming to Steem they need a way to get their Steem to their favorite restaurant or street market. Bitcoin is looking increasing clunky, expensive, and slow. Transactions often don't get included in the blockchain for a 30-40 minutes even with a decent fee. Steemit sends all transactions in <2 seconds. 

Steem is probably at .01% of network capacity (if that) and already sometimes doing more transactions than bitcoin (with far lower fees).

Now either those farmers-market vendors need to start accepting steem (which they can soon, thanks @kencode for BlockPay!) OR We need more fiat-crypto bridges separate from bitcoin. 

How can it be that we're still trusting a currency that is managed by pure PoW power. There is a huge wastage of power and it doesn't really increase the network security. Some if someone with millions of dollars just turned on a supercomputer and bribed one of the major pools to switch they could fake transactions or bring down the network. If someone with just a few thousand dollars blew it all sending millions of transactions across the network the crypto-economy would grind to a halt. This has happened before and will happen again. 

I noticed Ripple gateways added Bitshares, can someone explain how that works? Does it allow me to transfer Steem to Bitshares to Ripple to Dollars?