For example, I would very much like a ranking service which compares only coins that have:
- an own blockchain (similar to the "Coin" table on CMC)
Coin market cap has this option. You just have to select from the dropdown menu whether you want only coins or all crypto according to their market capitalization. I agree with you though since the first ranking to appear on the site is list of top cryptos and not coins with their own blockchain.
Yep, but the second condition I would like (to list only coins without a pre-mine) isn't available at Coinmarketcap.
Coinmarketcap has at least a "Filter non-mineable" toggle option. This filter takes out currencies where the supply is fixed (most of them based on a pure ICO distribution, like NXT or NEM) and so it filters "the worst offenders" in terms of premine. However, coins like Ethereum, where a big part of the supply has been premined, are still available in this list. In theory, even a coin which has a 99% premine could made "mineable". Another point I don't like is that this list is pretty much hidden.
What I would like is a "Filter premined" option, and the resulting list presented prominently as something like "Decentralized cryptocurrencies." or "cryptocurrencies without premine".