I Came across a blog post from coinbase that addresses  a  51% attack on the ETC (ethereum classic) blockchain between 5th -7th of this month showing chain reorganizations that includes double spends of around $1.1 million dollars.

Before that about $100k of vertcoin, $18 million of bitcoin gold, etc has been stolen in similar manner from different cryptocurrencies.

I am able to understand that this is due to the vulnerabilities in PoW consensus. It has also coincided with some calls for projects to switch to PoS

Here's are my questions:
1. How secure is PoS?
2. If its so secure why are most cryptos still running on PoW?
3. Does this mean that ETH blockchain is not as secure as it is said to be?