Suffix as defined in romanized Japanese morphological analysis


Older grammar books tend to rely on a lot of romanization to teach the nitty-
gritty of morphology, which is also reflected in some of @snail's answers like
[this one](https://japanese.stackexchange.com/a/12525/30454). I was reading
Samuel Elmo Martin's 1975 book _Reference Grammar of Japanese_ and noticed how
verbs are described (P. 308):

>   1. Transitivization, in which an underlying intransitive verb (such as
> kawak- 'get dry') is converted into a transitive verb (kawakas- 'dry it') by
> the addition of a suffix, here **-as-**.
>   2. Intransitivization, in which an underlying transitive verb (such as
> hasam- 'interpose') is converted into an intransitive (hasamar- 'is
> interposed') by the addition of a suffix, here **-ar-**.
>   3. Polarization, in which both transitive and intransitive are to be
> derived from some hypothetical basic form : e.g. naor- 'get improved' and
> naos- 'improve it' seem to be derived, by the suffixes **-(a)s-** and
> **-(a)r-** respectively, from a nonexistent verb *nao­- (etymologically to
> be found in the adverb nao 'yet, rather').
>

Just as @snail did in her answer, Martin also breaks up syllables/morae and
splits consonants from their pairing vowels when illustrating morphological
changes. Also he calls "-as-" in the word kawak **as** u 乾かす a suffix. In his
theoretical framework, a word like 乾かす has two suffixes, -as- being one of
them.

Hence my questions:

  1. Why is morphological analysis done at this level? Does it have to be done this way? Or is this kind of morphological analysis—anchored in romanization—a thing of the past?

  2. How is morpheme defined in Japanese? Nothing about its clear definition can be found on either the English [morpheme](https://en.wikipedia.org/wiki/Morpheme) Wikipedia page or the Japanese [形態素](https://ja.wikipedia.org/wiki/%E5%BD%A2%E6%85%8B%E7%B4%A0) Wikipedia page. Has there been more than one definition? Morphemes are supposed to be the smallest meaningful lexical item in a language, but in Martin's theoretical framework morphemes are not bound by morae or 仮名. This kind of morphology, it seems to me at least, would make sense in a phonetic and alphabetically based language, but the Japanese language had long existed before the language, the land, and the people had contact with alphabets and way before romanization attempts were made. It's almost as if no morphology is possible without alphabets and phonemic letters.

  3. How is suffix defined in Japanese morphology or morphologies I should say? The information available [here](https://ja.wikipedia.org/wiki/%E6%8E%A5%E5%B0%BE%E8%BE%9E) on 接尾辞 seems more intuitive and 仮名-based.

