> That every other vowel letter also can is English's low level of phoneticism
The level of phoneticism between English language and its latin script is not evenly spread.
For example, the letter "c" might mean /s/ or /k/ sound.
However, the letter "k" almost certainly means /k/ sound.
In some ways, the schwa sound in English the worst as there is no symbol which is committed even partially towards it.
> it is Rāma, and 'a' represents the schwa.
Sure, but if my name is Rāma, I have to choose either "Ram" or "Rama" or "Raama" for my passport name.
Or legal name in most places, non-alphabetic symbols do not work with all modern systems.
> Many other languages using the Latin script (German, Italian, Finnish) don't have this problem, what you see is what get.
English imports spellings from other cultures and adds its own layer of pronunciations.
Other languages probably don't do it as often.