This is indeed the one thing most people criticise me for, and I simply don't know what to do. Most fantasy planes, period, seem to get away with weird names and terminology and don't seem to suffer this issue. I've tried some reorganisation and simplification tricks before (compare the planes of Namacanaan to Matahouroa in terms of linguistic elaboration), but they didn't work.
Any special tricks?
The more crazy, "out-there" proper names you give, the more readers will subconsciously resist them. One or two? Not a big problem, especially if they're not very similar. But a bunch of them in a row, the mind tends to shut off and skip them, or sometimes resist the entire piece. Look at the canon planes. Apart from Dominaria, which has been meticulously established since the earliest days of MTG, how many are made up of more than three syllables?
Now, don't get me wrong, I'm not even suggesting changing Namacanaan. I actually don't think it's all that bad a name. But I have noticed that your names in general tend to be long, foreign-looking, and as CKY pointed out, difficult to figure out how to pronounce. Now, again, once in a while, that can absolutely heighten the fantasy experience to have names like that. So I'm not saying cut them out entirely. But once they start interacting with one another, or we as readers are expected to remember them, it get's increasingly difficult. It literally becomes like trying to learn a foreign language. One thing I tell my students all the time is "be as kind as possible to your Readers."
I don't know if you've read any of the Jade stuff, but she's a perfect example. Her "real" name is Nephractanini. How do you pronounce that? Where is the inflection? Are the vowels long or short? Is the "ph" an "F" sound like in English, or pronounced separately? When you use names like that, you are forcing your readers to stop and try to work these things out. Now, in her case, that was the point. She has a name that most humans can't pronounce, so she almost always goes by "Jade." It has storyline meaning, it's short, simple, and recognizable, and it helps the reader. Win-win-win.
So, the problem, as I see it, is not that you come up with unique names to fill out a fantasy world. The problem is that your narrative sort of "demands" that readers learn and memorize them all. Now, you are absolutely right. When I glanced through Matahouroa, I think that Namacanaan is a big improvement in that area.
Another thing to thing about is phonetics. Some sounds just work better together than others. I mentioned that the plane of Unaktil was slightly off-putting and awkward. After thinking about it, I think it's because of the hard "-ak" sound coming right up against the hard "T" sound in "-til". Compare, for example, Unaktil to Nakutil (I'm not suggesting you change this, mind you. Just for comparison.) The basic rhythm of the sounds reads more smoothly because of vowel break. With Bhamarivo, you have the two similar vowel sounds right away juxtaposed with change to the "-rivo" which moved faster and changes the sound. Again, these names are horrible by any means, but I think all five could probably be stronger. Shemaharesh, for instance, sounds to me like it really wants to be three syllables, like "Shemharesh." Just my opinion, of course.
A while back, Tevish wrote up an interesting thing on naming conventions in fantasy that was really good. I'll ask Lord Luna for the link.
Here (Thanks, Luna!). There might be something here to help!
But yeah, I would say the best trick I can advise is that if you're going to give them far-out-there names, also provide a synonym. So, for instance, with the Rahonafolk, be willing to simply call the Aven interchangeably. It helps.
Anyway, I hope that clears things up a little, or gives you some ideas. As far as the wall-of-text syndrome, my main suggestion is to use spoiler blocks to help break up the text. It makes it look a little shorter and makes the divisions even clearer.