What do you mean with doesn't have e or o? You can use Alif for them.
Present day Guayana would probably be called Arawakya or Arwakya.
Italics are for emphasis, not cynicism.
The classical Arabic
spoken language has three vowels /aiu/ which are distinguished only by length, diphthong assimilation, and pharyngealization. This is because Classical Arabic is one of the most evolutionarily conservative semitic languages (proto semitic also only had these three vowels). This is reflected in the letters written language as well. As the
script for Classical Arabic became used to write languages that do have those vowels, its Matris Lectionis were repurposed to that end. A rather poor choice in my opinion but then again what else would they have done? Dots on an alif look weird, and waw and ya are already dotted up.