Earlier quoted context omitted.
The te/ta-form is genuinely a separate system that doesn’t reduce further. I think there’s still value in having a solid model for everything else. At least I personally found it valuable, which is why I thought to share it with people.
I'm not totally sure this "stems and suffixes" mental model really works well for everything else. Forms like the imperative (食べろ), volitional (食べよう), provisional (食べれば), potential (食べられる), and causative (食べさせる) aren't cleanly handled either -- they work similarly for godan verbs, but you have to add a different suffix for ichidan verbs. It's definitely useful to understand how "chi" and "tsu" fit into the hiragana c…
They are cleanly handled in the final section (“one more thing”) that introduces a notion of disappearing consonant like -[r]u, -[r]eba and so on, and gives a rule for it. This is a perfect inversion of what happens with -(i)masu and friends. The hole in the stem accepts the leading vowel but burns down the leading consonant.
It’s quite elegant.