Also agree, you can already use combinations of multiple characters to define other sounds, and that's faster to type too
Shame, though, that in English the sounds that combinations of characters make, aren't well or uniquely defined (e.g. bird, word, hurt, heard, herd, ... all sound like the same vowel)
They're faster to type largely because your keyboard is English. Other languages (French, German, etc) have diacritics right there. Even Japanese isn't that much harder to type once you actually learn it (and, on fact, is quite pleasant on a smartphone even at beginner level).
On the topic of similar word sounds, this is a big thing that hangs up English speakers on romantic languages. Their vowels are sloppy and contextual, so when they're given explicit symbols that say "use this vowel", they struggle to pick that vowel out. That "symbol to sound" wiring isn't up in the noggin'. A Spanish person learning English will see the Spanish equivalent and go "duh". But an English speaker needs those "like in bird" tables.
Luckily, we have a huge phonemic index (because of all the stealing), so we're actually at an advantage from many languages once that hurdle is crossed. Spare tonality.
Shame, though, that in English the sounds that combinations of characters make, aren't well or uniquely defined (e.g. bird, word, hurt, heard, herd, ... all sound like the same vowel)