Bitcoin without exchanges would've never been this high in growth. Exchanges have played a big part, there are flaws as scams to ruin the reputation of bitcoin. In other way these exchanges have made more good to the uplifting of the market. As suggested bitcoin can function without exchanges, but we don't experience the same level of convenience and comfort as now.
My prediction of Bitcoin without centralized exchanges it would be a market with less volatility and less daily volume, the price would be about the same maybe, I am not sure.
With enough time the lack of convenience and comfort would have gotten solved, though. There is already one project of decentralized exchange for Bitcoin which I have heard of (Bisq), in the end if centralized exchanges never existed we already would have found a comfortable and easy way to operate, but we all got used to businesses like Binance and Coinbase.