Blockchains all have a bottleneck. All transactions in the world have to go through the miner. And the situation is actually worse than that because we don't know who will solve the useless Proof of Work hashcash function ahead of time, so EVERY potential transaction is gossipped to EVERY potential miner, and then the miners ALL go to town wasting electricity. How great!
Anyway, because of this architecture (preventing double-spending by literally aggregating all ambiguities into N potential histories of EVERYTHING, and then having them duke it out with PoW or PoS or any other way), we literally have a cap on how many "TPS" (Transactions Per Second) can go through.
Before Bitcoin, no one ever asked how many transactions per second an Internet protocol could support. It would be ridiculous to ask that of HTTP, or FTP or SMTP because there is no central bottleneck: the number of websites, files and emails that can be sent increases with the number of computers on the network.
With Bitcoin, Ethereum and other blockchain-based networks, this is not the case. The max number of transactions that fit inside a block is the most throughput you're going to get. The best thing to come out of these blockchains is Microsoft's Sidetree protocol championed by @csuwildcat but that's for identities, not currencies. So basically, you have a payment system which is super-secure and also super-wasteful.
It's as if BitTorrent required every computer to seed every movie, and BitTorrent maximalists called everything else that used a Kademlia DHT a ShitTorrent.
Except here, it's actually worse because you're not doing Proof of SpaceTime (like FileCoin) but you're requiring a growing number of computers to participate in a lottery proving they burn electricity and get rewarded sometimes. And this amount of computers is growing, just so we can do one operation (transfer money) 10 times a second. At least Ethereum made it into virtual machine capable of executingmore than one operation, thus enabling Turing-complete programming languages like Solidity, and smart contracts. Still, the way it's designed as a "world computer" it's basically a glorified mainframe, and gas is basically paying for time on the mainframe. It is the reason "flash loans" are even possible, they are artifacts of the idea that literally ONE transaction in the entire world can happen at any given time. Nice for atomicity guarantees, I guess, but overall not so great for almost every real world application.
Blockchains with global consensus about every transaction in the world are NOT what I would think of when I think "decentralized" in the sense of having no central bottlenecks. Actually @vbuterin wrote a great article years ago about the different senses of the word "decentralized".