This is a non-custodian wallet wherein a password can't be recovered if loss and you own your private keys.
You are 100% sure about that? You are 100% sure that their security set-up is unhackable? You are 100% sure that they don't have access to your seed or private key? You are 100% sure that they don't have access to your password? You are 100% sure that everything that happens in your browser is fully encrypted before being sent to them? You are 100% sure that they can't decrypt it? You are 100% sure that there is no backdoor or other malicious code anywhere on their website, backends, servers, etc? You are 100% sure they don't have any rogue employees who might want to push some code that compromises your coins? The list is endless. You have to take an awful lot on trust to use their platform. Not to mention that you are also trusting them never to freeze or lock your account, demand KYC, decide they don't like where you are sending your coins, and all the rest of it.
And you said one shouldn't trust Electrum wallet 100%, could this be because it's a hot wallet?
Depends how you use it. If you use Electrum on an internet-enabled computer, then yes, it's a hot wallet. You can also use Electrum as an interface for many hardware wallets, or on an airgapped machine, in which case it isn't.