Agreed with everything you said. Japanese pronunciation is easy to hit in the right ballpark because Japanese uses a near-subset of sounds found in English and other common languages. But refining your Japanese pronunciation takes effort and is not something to shrug off. Anyway, here are some examples where I think English-speaking Japanese learners butcher their pronunciation:
* し is [ɕi] (tongue fronter), not [ʃi] (tongue rearer).
* ふ is [ɸɯ] (mouth more open), not [fɯ] (teeth touching lips).
* お is [o] (monophthong), not [ou] (diphthong).
* え is [ɛ], not [eɪ]. (e.g. さけ)
* つ is [tsɯ], not [sɯ]. (e.g. つなみ)
* Anything with the Japanese r. The alveolar flap does exist in American English, though it's not consciously recognized as a distinct sound. Japanese sounds funny but still intelligible when the native [ɾ] is replaced with [ɹ] (English R) or [ʁ] (French R).
* Anything with small y (e.g. kya, nyo, myu) should have a quick [ʲ] sound, not a long [i] sound. e.g. きょうと is [kʲoːto], not [kiouto].
* Vowels are never reduced; きもの is [kimono], not [kəmounou].
* But the appropriate times to suppress vowels entirely. e.g. です, ～ます, して.
* The concept of doubled consonants, not grasping it.
* The concept of long vowels, not grasping it.
* Stress is often on the first syllable, not the second.
* Intonation is flatter than in English.
* How to use high/low/rising/falling tones correctly on particles.
* A natural and even pacing of syllables, not the choppy speech that foreigners seem to exhibit.