As far as I know we can earn ETH coins through airdrops, signature and bounty campaigns.
I think they are not directly giving you
ETH, they will give lot amount of coins where you have to convert them to
ETH. The only way if an altcoins project is successful then you can convert those
ETH.
I think there are Campaigns for other crypto too, not just
Bitcoin. But the easiest way to earn
ETH is from joining Signature Campaign. And then collect some
Bitcoin from those Campaigns, after that you can convert them to
ETH. Just like the way you said. I only know about Signature Campaign for
Bitcoin, I do not really know about Signature Campaign for other coin like
ETH. So, I suggest you collect some
Bitcoin to convert it to
ETH.