As some of you may know, auxlangers tend towards isolating languages. At the very least, the direct object is determined by word order rather than with a case ending (mostly because most West Europeans struggle to understand the accusative suffix in Esperanto). But reading through the Language Construction Kit 2, the author seems to believe the opposite, that fusional languages are easier (he argues they require less rules), and that children pick up agglutinating (though not inflectional) case endings sooner than they do word order (in that part he even explicately states: are you listening auxlangers?) He also has a segment the briefly covers Mandarin grammar, just to demonstrate that configurational languages are highly complex. He claims he shows people a book by the name of 'Mandarin Chinese: a Functional Reference Grammar', which is 700 pages long, to anyone who claims that isolating languages are easy.
But I've been wondering, are they actually any harder than languages with say case endings? I can see some things, like English tending to use words as if they could be any part of speech, and often times a word's meaning changes depending on whether its used as a noun, verb, or w/e.
But I fail to see how having the accusative be specifically marked really helps. If your language is consistently SVO, then any noun that follows the verb must be a direct object (of course things can get muddied if you have ditransitive verbs). If their parts of speech are marked, then why would an accusative marker be necessary? Other than permitting free word order. I could understand how someone who's used to speaking a language with subject and object markers could struggle with this, but really, people who are used to making do without such things struggle to make use or case endings or ad-positions that explicitly mark roles in a sentence.
Besides English (obviously), the only conjigurational language I've ever tried to learn is an Auxlang named 'Kah'. The grammar is obviously inspired by Chinese, though it seems highly simplified. At least it looks that way looking through the grammar. I've never learned it well enough to actually read texts.
Anyway, is Rosenfelder correct in saying that fusional languages are actually easier than isolating languages? He clearly seems to think so. I think at one point in his book he even states that a grammar of even a highly inflecting language full of irregularities has fewer rules than English or Chinese. He doesn't appear to know any inflecting language to any large extent. The only language (besides English), he really gives any indication of knowing is Quecha, which is an agglutinating language with case endings and polypersonal agreement on verbs. It would appear to me that it's also SOV, but pretty much all I know of the language comes from the sample sentences he gives in his own books (he mentions it quite often).
Personally, I think this would be hard to test. I mean, is there really a language out there that's neither isolating nor fusional? I don't see how such a thing could exist. Therefore, you'll find one or the other easier to learn depending on whether your own language is isolating or fusional.