Secured is a relative term. There are many people who don't trust wallet that runs in a web browser (such as the Steemit Wallet) and refuse to use them. The web browser itself is a pretty large attack vector for thieves trying to access your funds. This article regarding bitcoin "e-wallets" highlights some of the downsides to using a web wallet.
Basically, when using a wallet in your web browser, each time you enter your password or active key to transfer funds you trust that:
- The website has not been compromised to steal your information (or funds).
- That your web browser has not been compromised to steal your information (or funds).
- That your computer has not been compromised to steal your information (or funds).
When using a desktop wallet, you remove #1 and #2 from the equation, and now just have to trust that your computer itself hasn't been hacked. With that in mind, I would argue that Vessel, since it doesn't run in your web browser, is a more secure wallet than the Steemit Wallet.