From Subscrioption-Only LDOCE:

Yet means “it isn’t time to go yet”, while the still is a but is a but. It’s not the time to go yet.

Have you ever seen him?

What was used in the earlier situation and how it should be

used today is **Still* as it means the earlier situation ‘hasn’t changed’.

What do you still do that you don’t understand?

Why you would say in your final paragraph to use still, rather than yet, because you had thought and it hasn’t changed so far, and you are still thinking.

(from Subscription-only LDOCE):

That is often left out when it is the object of the verb in the relative clause:

They have not kept the promises they made (=that they made).

That can only be used as a relative pronoun to specify a person or thing, not to add extra information. When adding extra information, use who or which? She

had to look after her husband, who was sick.

Do native speakers of English sound lazy/parallel? Well in general though, that happens in all other languages. Since both are free software, you can choose which one you like (and follow the rules).