The biggest problem right now facing Bitcoin is the scaling problem. The current debate is between the "small-blockers", which support scaling bitcoin by limited block size increases and implementing off-chain transactions, and "large-blockers", which advocate continuous block-size increases. I personally don't think either method will scale in the long term, especially considering the original goals of decentralized digital cash. It is my opinion that both scaling paths force centralization of the network. This paper details Lightning Network, the current best design of off-chain scaling https://lightning.network/lightning-network-paper.pdf
OP makes the implicit assumption that all lightning network payment channels are p2p in which case the 20M users per month upper limit is true. From what I understand, the plan is to have a network of supernodes which settle on the blockchain. Users will interact with these nodes instead of true p2p. Lightning network opponents argue that these supernodes will become mini banks in some ways and will need to follow KYC norms. While it's possible to do p2p payment channels without interacting with any third party, the high transaction fees make it impractical. From the Lightning Network paper  :
> If all transactions using Bitcoin were conducted inside a network of micropayment channels, to enable 7 billion people to make two channels per year with unlimited transactions inside the channel, it would require 133 MB blocks (presuming 500 bytes per transaction and 52560 locks per year).
Notice the 2 channels per year. These 2 channels will be opened with a supernode (operated by eg- Coinbase, Gemini, Blockstream etc). I glanced through the document but they don't seem to acknowledge the requirement for these supernodes.
It's hard to cut through all the FUD, trolling, memes and propaganda to get to the meat of the debate, so I'm not too sure my understanding is accurate, feel free to correct me.
> and it's not bitcoin; it doesn't have the same assurances, there are some third-party channels that route the transactions. (I admit, I haven't studied LN in detail.)
lightning clients pass around bitcoin transactions to each other, check the protobufs: https://github.com/ElementsProject/lightning/blob/2bf92c9063...
admittedly the protobufs have changed since i last looked, here's the canonical diagram describing the hashed timelock bitcoin transaction concept: https://github.com/ElementsProject/lightning/blob/2bf92c9063...
or read the paper https://lightning.network/lightning-network-paper.pdf
> LN specifically requires segwit