Both solutions from Dash/Privex are handled with second layer solutions.

Absolutely not at all. They are all on chain with transactions being instantly locked by the masternodes rejecting any conflicting transactions with the already locked transactions. This is not a second layer solution.

I know of no completely decentralized solution that can scale on chain.

Check out EOS or Hashgraph.

There is a little bit of bias in the following subreddit+video but many of them are valid points. Plus we have better solutions than LN which is actually make the network less anti-fragile.
https://www.reddit.com/r/btc/comments/8n4209/why_the_lightning_network_doesnt_scale/