Due to this, I believe the best way to achieve the needed anonymity now is to use 2-3 different services.
If you use 2-3 services, you will pay large fees for services and for transactions, which will be unprofitable for you.
The easiest way to use the Monero ecosystem, but it's worth reading and understanding this useful information.
https://moneroleaks.xyz/If you have a point, despite the Monero ecosystem remaining one of the strongest options for on-chain privacy among major cryptocurrencies, it still not guaranteed 100% real world anonymity. Besides, there's also human error to avoid (like using a remote node over clearnet, which could lead to IP correlation, and the reuse of wallet address) when using it for total privacy, because no system is totally perfect, and to be on the safe side is the reason I suggest the use of 2-3 privacy services.
It is either you value your privacy, or you care about the amount it will cost to get the needed privacy, which is what many new crypto enthusiasts do by taking the easy route.
Not all coins are dirty, sometimes it is enough to use the DeFi ecosystem to exchange coins
DeFi or Dex?
DEXs, or Decentralized Exchanges, are the foundation of the entire DeFi ecosystem. Beyond DEXs, the DeFi ecosystem includes many other solutions:вridges, decentralized stablecoins(DAI,USDe,crvUSD) liquid staking, yield aggregators, perpetuals, and more.
If you are engaged in criminal activity, it's worth using several different services. Then the increased costs will be justified. But for the average user, this is an unnecessary expense.
No.
Decentralized Exchanges (DEXs) play an essential infrastructure roles, and it is consider as the cornerstone of DeFi due to it roles in the area of liquidity. However, it is not the single foundation of the entire DeFi ecosystem, but blockchains and smart contracts are the foundation of DeFi. Besides, everything that includes the DEXs, lending protocols, yield farming, etc. is built on top of blockchains and smart contracts.
You don't need to engage in criminal activity to use a 2-3 privacy service, you can use tumbler and a private wallet like CoinJoin.
Yes and no

What do you call a cornerstone?
AI:
"A cornerstone is the foundation, the main element, or the most important essence of something, upon which the entire concept, idea, or system rests."
If you agree, then thanks for the addition.
Decentralized exchanges may not have their own liquidity at all, allowing you to get started without the initial capital required, for example, to create a pool on Uniswap.