I agree with that, but we now that everything in the internet can be hacked. I know that blockchain and in general web wallets builded to be highly secure, but that doesn't mean that bitcoin web wallet are safe lifetime. I am pretty sure that one day, I will hear that someone can hack a web wallet, because there is some genuis hackers in the world when we talk about black hat for exemple.
So, in conclusion, I can agree that web wallets are top secure, but i can say that is not impossible to hack them.
BULLSHITWeb wallets are about the least secure method of storing any amount of Bitcoins, even if 2FA is enabled. If they have your private key, they can do anything they want. Most wallets advertise themselves as not having access to your private but they do infact, may have copies of it. They can easily update the UI and trap your passwords or seed to unlock the wallet.
Google around and you will find numerous hacks on web wallets.