Hi this is Bobby, co-founder of CoinGecko. We don't claim that our ranking is the best but we want to help the community by providing more metrics to better analyze altcoins. That's our main objective.
I agree that there are more metrics that we should consider and we plan to add more metrics as we go along. The community section is highly skewed by using data from Reddit which I agree doesn't reflect coins used in non-English speaking countries such as
Monacoin (popular in Japan) or
Ybcoin (originating from China). That being said, it still provides a basic method for looking at altcoins.
For developer, we actually take stats from Github and for those hosting their source code on Bitbucket, we get the stats there. Coins which do not have open-source code repository will have a score as 0 as we cannot evaluate these coins. Coins need to have their source code open for others to check for bugs and ensure that the code does what the coin creator claims.
Hope this help answer your concerns.