Then Layer 2 (Lightning Network) is practically the solution to this fear of Bitcoin's supply or decimals having to be modified. Right? There are so many threads talking about the issue but never have I seen this solution suggested or talked about.
In its current form it would only be part of the solution. There are still other stumbling blocks which would need addressed first.
Let's say that a satoshi is worth $1 or more. Are people going to be happy spending hundreds of dollars worth of bitcoin just to open a channel? Or do we need something like channel factories to make it possible to open a channel for a fraction of that cost? And more importantly, what about if you have an amount on your channel which is currently considered on-chain dust, but which could be worth hundreds of dollars? Most people won't be happy chalking that up as a loss.
Although it is worth repeating that for a satoshi to be worth $1, then the marketcap of bitcoin would be $2.1 quadrillion, which is more than an order of magnitude more than the global monetary supply. It is a crazy hypothetical.