EOS plans on "parallel executions" can SIDECHAINS do this?

The Bitshares and Steem whitepapers describing the Graphene engine only talk about rather local optimizations when describing how they can achieve thousands of transactions per second. In this context, this metric would rather compare against Oracle clusters and the like (where they would lose, of course, impossible to compete with decades of domain knowledge in this field).
The question about the security trade-offs when achieving their transaction throughput, which is the actual issue to look at in the blockchain domain, is left unaddressed. Or, to put it more simply: Why is it a blockchain at all? It's just a database engine. Bitshares, Steem and probably also EOS are run by a fixed and known set of 20 or so validators, also known as "witnesses", probably consisting of Larimer himself and closest cronies, who will of course never behave maliciously. They can be voted in and out by "the community".
This has not much to do with Satoshi's invention after all. There is no decentralization. If you remember that famous centralized-decentralized-distributed graph, the "decentralized" graph is intended to look self-similar no matter where you pan and zoom. This is not the case with Graphene. You zoom out, and you'll have the 20 nodes in the center.
At best there is a niche for this approach, at worst it's intentionally misleading and a scam. The truth is maybe somewhere inbetween, but then you have to ask what's the technical benefit over a centralized setup ???
Thanks fo your time . What do you think ???