700 or so is listed on coinmarketcap and 100 coins are over $1 million marketcap. Still, most of them offer nothing interesting and are waste of time and effort.
I don't think they are a waste of time and effort. Like in all innovative tech, most of what you do, fails. But without all the failures, the good ideas wouldn't emerge either. Thinking that a monopoly works better than a free market, is somewhat strange for people that think "distributed, decentralized, trustless". As of now, bitcoin is more or less holding a monopoly on crypto. Its tech is getting old now. There are many more sophisticated crypto ideas around, like ring signatures, zero knowledge proofs, smart contracts, proof of stake versions, directed graphs instead of chains, .... There are also experimentations with flexible block sizes...
Bitcoin starts looking like the state telephone company holding the monopoly over telephony, while mobile phones are being invented.