Did Bitcoin founders know Bitcoin is not scalable at Base Layer?
If you look at the announcement of bitcoin and the very first response to it, you can read James A. Donald pointing out that bitcoin (which we today call the base layer) &quot;does not seem to scale to the required size&quot;.
Partial quote of James A. Donald's response:

We very, very much need such a system, but the way I understand your
proposal, it does not seem to scale to the required size. [...] hundreds of millions of people are doing transactions, that is a lot of
bandwidth - each must know all, or a substantial part thereof.

This response was sent more than two months before the genesis block was mined. Thus, it is fair to assume that Satoshi was well aware of the scalability concerns.