I do agree with the left to right thing because, well, due to the way English is, it's quite hard to read right to left in languages like English.
Even if the comic is "manga-inspired", I don't really see a big deal in calling it manga? It's just a word that means "comic" but written in a different alphabet. Sometimes, the English romanisation of the word may be used in a slightly different context than it's original language. Loanwords exist. These actually happen quite often. A Chinese to English example I can think of is cheongsam, which literally means "long garment." But I've never seen or heard anyone actually call them "long garment" in English, just cheongsam (or qipao which is another name for it and that's also a loanword). Arguably, I've heard "Chinese dress" before but there are many different types of Chinese dresses. When you get specific, are you talking about the cheomgsam or the hanfu? Well, hanfu literally means "Chinese dress" but I've only ever heard people call the cheongsam a "Chinese dress" because well, the hanfu seem to be less known, not to mention that they aren't usually worn in general these days. So are these people wrong? If you mean the translation word for word, then arguably yes, but when the word is used in another language, it may not be easy to adapt the word into the other language so that the word is used in the exact same way. Either way, I'm not bothered by it. I don't see it as "disrespecting my culture" or anything, it's just the way language works. The reverse also happens from English to Chinese. For example, 多士 is a phonetic translation of the English word "toast". I mean, why not call it "heated bread" if that's what it means?
I think those "weaboos" you're describing only make up a small portion of people who like Japanese stuff. I know a lot of people who like various Japanese stuff (mostly anime and manga if I'm being honest) but I have never met anyone who are hardcore weaboos like you've described?
I'm not quite sure what you mean by this? I'm pretty sure you can like more than one culture at a time. I also don't see a problem if you prefer Japanese media, it's not like you must prefer the media of your own origin. Not gonna lie, I don't like most Chinese media. Not that there aren't occasionally decent stuff though.
My conclusion: manga in the west loosely means Japanese comics and it's not as deep as everyone is making it to be. If people want to call their manga-styled comics manga, then they could call it manga. (I'm not Japanese so if anyone with sufficient knowledge of Japanese language/culture would like to correct me, please do.)