<< Bitcoin is too expensive ... >>
That is a common fallacy, since an investor doesn't need to purchase an entire bitcoin. They can just buy as much as they want.
<< ...and less attractive at the main stream consumer level to be adopted for retail payments >>
Both BTC and SHIB will most probably not be used for a large % of retail payments, since their prices fluctuate too much. Nobody wants to receive payment for something and then see that money depreciate by 50% in a few months.
Retail will most probably use stablecoins of some sort (USDC, USDT, BUSD, etc). The US dollar (USD) will also most probably be replace by a US-backed stablecoin at some point in the next few years.