What do you think about Bitcoin's scalability today? Do you think the bitcoin network is scalable enough to confirm hundreds of millions of transaction in minutes assuming it's the only network that exist in crypto and we all have to use it.?
Satoshi's statement is clearly an endorsement of second layers. Not everybody has to store and verify the whole blockchain history!
Both Lightning and Ark are
mechanisms to use the blockchain only in the cases we need a double spend protection because there is a dispute between two users. "Normal" on chain transactions are a luxury: we use the double spend mechanism even if we have no intention to double spend. That's why scalability "looks" so hard now.
But yes, most methods have tradeoffs.
Lightning's problem is that it could handle the payment volume of hundreds of millions of users, but it would take years to onboard them (actually, it could onboard about 40 million per year). Users can share an account, but with pure Lightning it is then difficult to handle disputes correctly, which would mean involving trust again - subverting the
Ark is a variant of "Lightning with account sharing", in some form. So it has a much higher capacity. However, if the capacity of Ark is scaled too high, I imagine there will be problems when too many people want to use the unilateral exit. So I believe that the number of "billions anually who can be onboarded" has to be taken with a grain of salt.
The most scalable concept is probably sidechains. Sidechains do not provide an unilateral exit, they are more like Bitcoin stablecoins with a peg mechanism. But their capacity is really in the billions/year order of magnitude. But there are "not pure Bitcoin" because they rely on additional security assumptions, like a second consensus mechanism (even if it's merged mining, it's not 100% the mining security of the main chain).
