I think you summed up the most important grammatical concepts nicely. Though I think you have mostly looked at indo-germanic languages, and all these tend to be similar. If you go beyond these languages (e.g. Basque, Hebrew, Japanese), grammar becomes a lot more varied and weird.
BTW, the German word for "command" is "befehlen"; "fehlen" means "to be missing". "Fehlen" and "fail" not only sound alike, they are indeed etymologically related (Latin "fallire", French "faillir").
I would agree that the subjunctive is related to uncertainy and doubt. But at least in the languages I know, giving a command (a very definite and certain mood) is not done in the subjunctive. Expressing a very polite wish is, because the less definite and more uncertain and roundabout the talk, the more polite it is perceived. (BTW, this also works in languages like Japanese that don't have a subjunctive, where you start to use double negation and other things to appear more polite).
Also, in the indo-germanic languages I know, the usages of the subjunctive always include reported speech and a variant of expressing wishes, hopes, doubt, or other uncertaint things. These are often clearly separated; e.g. in German the former uses Konjunktiv I, the latter Konjunktiv II. The former is subject to strict rules for tenses in English, the latter isn't. Conversely, for conditional sentences (some of which uses the subjunctive), in English and French there are strict rules for the tenses.
So I don't think it makes a lot of sense to lump these two aspects of the subjunctive together, it will make learning the appropriate rules only harder.