Great insightful comment, I've never really typed on anything but an IME keyboard on a computer, so I wasn't familiar with how easy it is to type kanji / hanzi on a phone
IME keyboards (for Japanese) has always confused me, since sometimes if you input hiragana or katakana it would translate to the kanji equivalent because japanese is kind of weird in that they have 3 written types. Thats just a quirk with Japanese itself though. I'm am glad that English doesn't have such an issue though. Then you have Romaji, the English - Japanese phonetic equivalent
Its also important to note when doing these comparisons, Japanese has a significantly lower information informational density than that of other languages. It also has a low reading speed rate too (informational rate), but very high speech rate (e.g. how fast you can talk with the language). English is actually very high across the board.
https://www.quora.com/Whats-the-most-efficient-highest-infor...
The article here has an image of the table I am thinking of (its the first response) for the data, from lyons et al. But, it does omit certain languages that are of interest as well, namely arabic. The rate at which you can write arabic and achieve the same level of information by hand is very closely related to that of English shorthand https://en.wikipedia.org/wiki/Shorthand. This might not tie directly to texting, but its worth mentioning because notetaking efficiently requires quickly capturing information. Some people prefer by hand others by typing etc
I don't really know all the slang terminology in Japanese all that well, but in English we have things like brb lol btw lmfao roflcopter fam. I don't really know what the Japanese equivalent at all of this is, and I wander whether if you were to compare Japanese Slang to English slang / Ebonics, which input type method is superior on a phone? The japanese flick input method or a traditional qwerty keyboard. My bet is on the latter though (QWERTY)
Like I know instead of saying わたしは you could just shorten it to ぼく は (only if your male though). Which means "I am ..... {{doing something}}". You could just say instead "{{doing something}}" too, which gets the same point across. In mandarin you would use 我是 which is pinyin is typed "woshi" which is the equivalent.