This is just not true. The host serves data to a client which can do what it wants with it. The client can interpret the data from the website however it wants

This is just not true. The host serves data to a client which can do what it wants with it. The client can interpret the data from the website however it wants regardless of the intention of the website. A website, for example, can use tags that a client doesn’t comply with. The client is and always has been opinionated. It does not and never has had to obey the websites intentions.