I was oversimplifying... As in having more miners means faster increase in blockchain length as they are essentially mining blocks containing their own previous mining profits.
We all have read stories about very long alternative blockchains due to having too many miners and mining pools getting out of sync for extended period of time.
PoS is more wasteful for new users as it requires to have some coins in the first place, PoW doesn't have that requirement. What we need is third option that doesn't have the cons of the two existing ones.