Latin diminutives are easy, they all follow exactly the same pattern, with the possible exception of the fifth declension in which there are a couple irregular forms, but that's because it's a rather archaic form. First and second declension nouns simply add "-ulus, a, um" to the stem. Third, fourth, and fifth declension regulars (like, 99.99% of all words in those declensions) are also very easy, you just add "-culus, a, um" to the stem (or very rarely "-cell-" or "-cill-" but those are very uncommon). The only weird thing that regulars do that I can think of is that there's a change in the diminutive ending after vowels from "-cul-" to "-col-" which is a pretty common change in Indo-European. And it doesn't matter--you don't have to have a degree in Classics from Harvard to tell that a gladiolus is simply a diminutive of gladius. Other than that it's very simply--most diminutives are in the first/second declension nouns anyway, and there are only a handful of irregular forms, which are rather common and easily recognized (lapillus is the diminutive of lapis, homollus of homo, etc. Many of these operate according to known linguistic principles that are easily predicted if you know them--homollus, for example, results from the assimilation of the "n" in the stem "homin-" into the "l" of the diminutive ending)

outrageous latin declension systems

Nah, Latin's noun inflections are easy. Only three real declensions (the fourth and fifth are actually obsolete and dying forms) and almost no irregulars. Try Greek--there you get a hybrid declension and the third declension is actually several different declensions that share the same endings (but whose stems change radically). Plus you get to deal with contractions, alternate ending forms (goddammit Athenians, always spelling things however the fuck they want) for a single case, irregulars up the wazoo--oh, and in a couple noun types the Greeks just for some reason decided that they were going to ignore the strict rules of vowel contraction and spit out a random-ass ending just because they didn't like the way the actual one sounded or something. Or better yet, try Sanskrit, where you get all those problems (and then some), plus the swimmingly convenient fact that in the case of hiatus they don't just contract the noun, they actually stick on a completely different ending that shouldn't exist! Yay!