In this altcoin sector, I prefer to call them air coins, because sometimes they are invisible and intangible, and sometimes they disappear without you being able to track them.
I sorted them into categories: mainstream altcoins, non-mainstream altcoins, and junk coins.
You can choose this on your own but I do not see the point reclassifying them into these categories. High caps, mid caps, low caps, micro caps, should be fine. Scam or fake coins would address your junk coins.
Mainstream altcoins have different functions, different founding teams, and have a strong trust endorsement, a strong technical team, giving us enough confidence, I can accept it, for example, Ethereum, Monero, Litecoin, etc. . Non-mainstream digital currencies also have a relatively strong trust endorsement, especially the founders who dare to innovate continuously on the basis of Bitcoin, especially in the field of DEFI and NFT, which are also acceptable by many people, such as UNI, SUSHI , FTM, CRV, etc. The rubbish coin is pure violent marketing. There is no well-known team, no economic model, and pure plagiarism. Some will not give you tokens, and some will just run away. The entire publicity process is simple and rude, with one purpose: please Add bitcoin to my wallet address.
[/quote]
You are trying to redefine the meaning of mainstream. The basic definition is "accepted by most people". Monero may be popular among crypto enthusiasts who likes true privacy and anonymity but it's not accepted or supported by many investors today. We have different views on Doge but it became mainstream even if it doesn't have a strong technical team. That shouldn't be the case if we go by your definition.