Our "schwa a" is a very flat, somewhat extended ah, verging on aah; you have to momentarily widen your mouth, as if into a smile or grimace, to say it. It's not a posh, round-mouthed aw, nor a dropped-chin doctor's "ahh", not a grunted uh, not a clipped o'h, not a rhotic ar, not eh, not er, nor any other of dozens of other permutations. But here I am, trying to _describe_ it to you; it's almost futile. If I had training in the dictionary sybolism you use, I might succeed, but anyway I'm still not convinced that the sybolism has standardised sound correspondence.
Ah, well, you are entitled to your opinions, of course, as am I, but the IPA has been used for quite some time by linguists and phonologists to represent how folks pronounce words in their languages and dialects, and it does a damned fine job of it. What with your non-IPA transcriptions of various kinds of schwas, I must admit I would have to hear you say them to tell you whether any or all of them are different nuanced pronunciations of a schwa or some other vowels. There are diacritics that can be added to most of the glyphs in the IPA to fine-tune the pronunciations. After that spectrograms can be used if finer gradations are needed.
The IPA is not a mere dictionary symbolism, it is a way to accurately represent the varying sounds of different languages and it does a good job at that. It's better than ad hoc pronunciation guides based on the erratic spelling 'system" of English or any other language. It's not perfect, but somebody who knows some phonology (articulatory and acoustic) and the IPA can give and get a good idea of how words would be pronounced in various languages and dialects.
