You do not have control over your private key just like coinbase and other centralized exchange.
Unlike most web wallets, blockchain.com does actually let you access your private keys and seed phrase, and export them to another wallet if you so wish. So although you do have control over your private keys, there is absolutely no guarantee that you have
sole control over your private keys. Blockchain.com
say they don't have access to your seed/keys/coins, but since their platform is completely closed source, you are trusting them completely on their word.
Otherwise, blockchain.com still suffers from all the same flaws and security risks as other web wallets. They have been hacked repeatedly and have had a number of serious security flaws which resulted in users losing large sums of bitcoin. They should be avoided, like all web wallets.