You're saying that there should be such a thing as a "proper scientific conclusion" to this meme about a video game physics engine? The only definition of these portals that we have to work with is the definition in the Portal physics engine. There is no definition of anything that behaves like these portals in the scientific study of physics. It is meaningless to try to draw a scientific conclusion about something that does not have a scientific definition.
Sure, I do think that's a reasonable difference in opinion and I agree that it's mostly fine for someone to dislike the way that a language is changing. I think the trouble comes in when that dislike is framed as though it comes from some position of authority or superior fluency, since it's actually an emotional argument, not a logical argument.
Your feelings about English are valid and meaningful, but only to the exact same degree that my feelings about English are valid and meaningful. Telling someone that you don't like the way they're speaking is often rude, but it's not false, because you are the authority on your own feelings. Telling someone that they're speaking incorrectly is usually "not even wrong", because it's framed as a logical argument but it has no logical basis.
I don't agree that it decreased the total expressiveness of English, no. The modern colloquial use of "literally" is not identical to "figuratively", or to "very", or any other word I can think of - it's an intensifier with a unique connotation that doesn't have any good alternative. At worst, we have lost some expressiveness and gained some expressiveness, and there is no objective metric to decide whether that's a "net positive" or a "net negative"; it's just a change.
Why is requiring more words inherently worse? Are languages that require more words to express an idea worse than other languages which require less words? For example, English has lots of prepositions whose meaning is sometimes instead encoded by verb conjugation in languages like Spanish (e.g. infinitives requiring "to" in English but not in Spanish). Does that difference make English worse than Spanish?
The problem is that there is no universal "currently accepted way of doing it". What you're describing is a dialect. It's sometimes reasonable to say that a certain use is wrong in a certain dialect, but insisting that a certain use is universally wrong is just insisting that your dialect is somehow more authoritative than other dialects.
There is no absolute prescriptive authority on the English language. It just doesn't exist at all. The common English dictionaries don't claim to be prescriptive authorities, they claim to describe how the language is currently used. If there are any English dictionaries that claim to be prescriptive authorities (I don't know of any off the top of my head), they're clearly completely ignored by pretty much the entire world of actual English speakers, so their authority isn't worth very much.
I strongly disagree that slowing down the change of language is nearly entirely good. I think it's neutral when it's a natural slowing caused by cultural shifts, and I think it's strictly a bad thing when it's a forced slowing caused by active gatekeeping from self-appointed dialect police. Language is inextricable from culture, so language change is inextricable from cultural change, so language conservatism is a form of cultural conservatism.
If I had a crystal ball and I looked a couple hundred years into the future and saw people speaking the same English that I speak today, I would be terribly sad about English-speaking culture. I sure hope we have new ways to talk by then! I also think you're dramatically understating how much English has changed in the past couple years - while English from the 1700s can mostly be deciphered by modern English speakers without a complete re-translation, it certainly doesn't read fluently to a modern speaker, and it's missing a whole lot of the words and structures that people use to express their modern concerns. This is all normal and natural for a natural language.
You say this like it's a fact that the word "literally" is worse now than it was before its recent evolution. You're reducing the entire value of a word to a metric of "clarity"/"muddledness", but natural language has value beyond its ability to be technically precise.