When my account gets serious would I be better off using a dedicated wallet exchange like
blockhain.com - I bought a few hundred pounds of BTC on 2017/18 and like an idiot I cashed out
when BTC was trading in the 30's But still made a useful amount.
It's always better safe to move your funds from the exchange balance to your own wallet which you hold safe the keys. For bitcoin, i would suggest Bitcore or electrum as they are friendly use and compatible with less-experienced users.
Note that blockchain.com wallet isn't just an exchange wallet, as it can be used as a personal wallet after exporting the seed. But better not to use online wallets and choose one of the clients I've mentioned above.