This has been one of the wrong mind set the new beginner in the cryptocurrency space are failing to understand, the backing up seedphase of a wallet on google drive is like making it more faster an easier for scammer to attack the wallet,
When we talked about avoid a third party, this does not only applies to those you have a physical contact with that can steal your coins, any online centralized platform is also a third party and should not be allowed to have the opportunity of holding on our private keys, they are not saving them, because they have a central server all these information are stored and they can get across to them at anytime as they demands.
Third parties can never be trusted with any private information such as seed phrase because they can not guarantee their own safety talk less of their customers or clients. It is never advisable to give access third party exchange your wallet seeds because their data base is being manned by somebody which means anything cam happen and there is nothing anybody can do about it. If is better one saves their keys by themselves in a secured place than to put it in custody of an exchange that can not guarantee their own safety.