they've lost their meanings but not in the way you think they have. Lolisho and incest ships were included in proship but it never meant that you had to ship those things, it just meant if someone did just doesn't harass them. Over time, it did somewhat include overall anti-censorhsip in fandoms due to the fact that many people for some reason are trying to censor fandom content for being "problematic". It's where the branch "pro-fiction" comes from.
Now "pro-shipping" has weirdly political ties such as being liberal, anti-conservative, etc. to them.
Anti did somewhat originate in the kpop fandom in reference to hating a particular person in a group and it did mean anti-shipper. And you're right in that they're people took shipping too far and harassed other people for it. That said, if you harassed people for lolisho, incest and other problematic stuff even by old fandom standards you'd just be considered an anti or fandom jackass. In fact, in "old" fandom it was incredibly common to ship incest (usually twincest or siblings like the Hitachiin twins from Host Club) or something that bordered on lolisho (such as Toshiro and Rangiku from Bleach). The only people that gave a fuck were people who didn't like that ship in particular. You could also just like problematic shit without people being up your ass about it.
The entire war is stupid I agree. My personal theory is that with the internet being sanitized and too many children not being told how to actually interact with content that they don't like. Or even the expectation that fandoms are intended to be a space for children and the idea that if you like something in fiction you must condone or like it in real life. Fandoms used to just be "antis" and everyone else because everyone else just left everyone else alone. For some reason, on both sides shipping has been tied up with activism and IRL morality (more so on antis in my experience because they're doing the same shit, different tactic. Rather than just calling a ship stupid it's abusive, problematic, etc.) and more pro-shippers (few as they are) mention what you ship or do in fandom doesn't reflect your actual morality unless you are actually doing fucked up shit to a person. Antis just learned as long as you can appeal to emotion and have to "make things safe" for children then accusing you can accuse of being an abuse apologist because they read Killing Stalking then fewer people will oppose it because if you oppose it, it means that you are an abuse apologist not that you are a person who knows how to curate their own media.