I'm surprised that you don't put decentralization at the heart of cryptocurrency. Yes, cryptocurrency has crypto-based encryption at its core, but the original idea of cryptocurrency was that you don't need to trust your money to a third party. And the centralized system is in fact a third party. So you're wrong to say that cryptocurrency shouldn't have decentralization.
If decentralization is the heart of cryptocurrency, the coins listed on CMC or Coingecko might be around 10-50, not 2K. Because 95% coins are centralized and it shouldn't be included as a cryptocurrency, then why it's included?
I don't see any other trusted decentralized coins except Bitcoin, Monero, Litecoin and DAI. There's a decentralized coins, but the marketcap is small and has higher chance to suffer 51% attack.
I'm not saying centralized coins is good, but I just want to be fair.
To put it bluntly, the cryptocurrency market is a financial market, and what many people are interested in participating in is profit, only a few are interested in the technology and use cases. So, I also disagree when saying that decentralization is at the core of cryptocurrency. If everyone were centralized and only interested in decentralization, then altcoins would never exist.
I don't use XMR, or LTC very often, so I don't know if they are really fully decentralized. But if someone is looking for a decentralized and secure coin, the only thing I can think of is bitcoin.