that is a common mistake most people make about altcoins! being popular "brand" and being on top of the lists doesn't make the coin good or even profitable. there are lots of much better coins that aren't that popular. in fact popularity of an altcoin mostly means it is a bigger pump and dump.
as for market cap, it is so arbitrary that it is meaningless. the first thing that having a high market capitalization shows is that the said altcoin has a huge circulating supply with a big percentage of premine. take the biggest altcoins ETH and XRP, both of them have huge  supplies and both have huge premines (70% and 100%) and big part of those coins are in control of their centralized power.