Is it really a modern thing ? Somehow we got from Beowulf to Shakespeare, and from Latin to French in the past. I feel like the concept of “freezing” language in some fixed form is the more modern and academic ideal - and quite a quixotic one at that - people on the street will do with the language what they will as they always have.
Majority of the time when someone says they’re jealous of something they absolutely mean envious.
Isn’t this how language works ? If majority of the time people use the word in certain way, than that becomes one of its accepted meanings. In fact dictionaries list one of the meanings of “jealous” to be “envious” (with citations of this usage going back to 14th century, including works by Oscar Wilde and Mark Twain that are over 100 years old)
I am not sure you were as wrong as you think - see definitions 2 and 3 here
Usage of words shifts and sometimes expands over time.
I would personally definitely interpret “apparently” and “plainly” differently - “apparently” to me is “the evidence so far does seem to point this way, but I am not necessarily convinced, or have strong feelings either way” vs “plainly” is “the evidence is clear, I am convinced, and so should you be” - although obviously context would matter as well and could alter this interpretation.
Edit: even your example usage “I’ve been trying to get myself out of that habit, but even judging from my comment history, it’s apparently pretty hard” - to me the usage of “apparently” here indicates similar tension and/or contradiction, in this case between belief/intent (I am trying to stop the habit) and evidence (but my comment history shows otherwise) - it wouldn’t work quite as well with “plainly”
It would work with “evidently” but carry more of a connotation of confirmation and shift the emphasis (I am trying to, but it’s hard as confirmed by evidence) rather than contradiction (I would like to think I am doing it, but evidence shows otherwise) - of course you might have meant it either way (or even neither) - I am just saying how it reads to me.
I do understand the sentiment. I am a bit old and have seen words and phrases shift meanings in my lifetime and feel occasional irritation due to it (although I try to care less and less about it :)
I do find it harder to get worked up about a word that acquired additional meanings in the 14th century though - that ship has truly sailed :) Like who am I to school Mark Twain on the meaning of words.
I also find the ability of English to use the same word with different meanings and the power of context quite interesting (the fact that individual words exist in English with 100s of distinct meanings is really quite mind blowing.)
Ideas and concepts can sometimes be fuzzy as well with large overlaps, and insisting on too much specificity, precision and delineation in the language can be counterproductive to effective communication just as much as allowing too much flexibility can - but yeah, I guess there will always be some tension there and differences of opinion.
Language is often messy, but always fascinating. (And btw, I never said good or bad or right or wrong - I don’t feel it’s really my place to place such judgements)