So does it means that Zilliqa has PoW consensus? In this case their speed should be too low as like as Ethereum has?
You are right most of the companies are developing their model from POW to POS because they want to increase their transaction speed. Now Ethereum has already begun its reputation to develop the POS model in order to speed up its transactions by speeding up the node activation. We have to wait and see how Zilliqa reputation once ETH 2.0 Launches.
Having been involved in ETH for around 5 years i know alot about both both ETH and Zil.
ETH had began its journey to POS years ago, it wont ever go full POS , it possibly will go to POW/POS hybrid.
Also Zilliqa has other benefits over ETH, like its smart contract language Scillica(OOPSLA approved) is alot safer and easier than Turing complete Solidty.
Here is me promoting POS coming to ETH in Jan 2016 when it was around 70cents per ETH.
https://bitcointalk.org/index.php?topic=428589.msg13542129#msg13542129and here is me telling ETh community about the DAO hack news 3hours after it happened (not possible on Zil,Scillica)
https://bitcointalk.org/index.php?topic=428589.msg15248065#msg15248065