S&P 500 E-mini futures have a notional value of roughly $147,000 right now, and on average, 1-2 million contracts change hands daily.
On average, about 35 billion dollars of SPY, a single S&P 500 ETF is traded daily.
It's hard to find accurate BTC average daily volume numbers, but probably somewhere between 1 and 10 billion dollars daily.
So yes, bitcoin is an extremely thin market compared to the market depth of 2 extremely liquid assets, both of which pale in comparison to the 550 billion USD daily volume of the treasuries market.
BTC does have the tightest bid/ask spread of pretty much any asset that is traded, as a percentage of the asset's value. It's typically a penny to a few cents on the major exchanges, which is a few thousandths of a percent.