if I'm being honest I never really cared for series 8 or 9 & mixamajig was such a mess I can barely remember which tribes belonged to which series. and tbh if the royal idiots didn't take up more of my brain than I'd like them to I probably wouldn't have bothered to care about any of year 3 this franchise peaked at series 4 - 🎵
Honestly I completely agree with you, not just because of my huge bias towards series 4 but mostly because of the massive drop in quality of everything post-M3. Mixamajig was pretty weird, alot of the characters acted nothing like how they were described in the Lego descriptions, not to mention the massive abundance of animation errors, it's pretty easy to tell it was somewhat rushed. Sure, some parts of Mixamajig may still be salvageable, but I think the best way to fix it is to almost completely rewrite it or something, maybe split it up into two separate specials so we don't have to introduce two whole waves worth of new characters in a single episode, that way everyone gets a fair amount of screentime.
EKHID is probably the best of the Post-M3 episodes IMO, it had the closest animation to the older episodes (using the Chad smooth and clean flash animation over the Virgin weirdly gritty sloppily "hand-drawn" animation), the story was decent, and they didn't try to cram in more than 9 new awesome characters to collect and build in one episode. Of course EKHID does indeed have it's flaws, the noticable absence of Tapsy, the fact that some of the background Mixels had a bigger role than characters with actual sets, and the fact that Camillot's dad really sucked at his job of being a good parent, but in comparison to the other two Post-M3 specials, EKHID's issues aren't nearly as bad.
NNGA is like if you took the worst aspects of both Mixamajig and EKHID, turned those bad aspects up to 11, put them in a blender, removed the entire point of Mixels from the plot, and basically gave it such a boomer message of "phone = bad". NNGA is littered with animation errors (from what I've been told it apparently has more errors than Mixamajig), the protagonist of the episode not only acts completely out of character from how they've been previously established, but they also made the protagonist a LITERAL BACKGROUND CHARACTER. This background character, who I should probably mention is Booger from the previous episode EKHID, is also a complete Gary Stu, meanwhile a bunch of the characters with actual Lego sets have ironically been reduced to mere background characters, which is honestly just really depressing for long-time fans like myself. LOOK AT HOW THEY MASSACRED MY BOY, POSSIBLY EVEN LITERALLY SINCE SOME PEOPLE THEORIZED THIS STATUE IS A MEMORIAL ONE IMPLYING THAT NIKSPUT IS FUCKING DEAD!
Anyways getting back on track, another cardinal sin of NNGA is that it just, doesn't even feel like a Mixels episode. The characters barely Mix, they don't use the power of mixing to finally defeat the Nixels once and for all, instead we get fucking COORDINATED GROUP DANCING and Gay Laser Big Chungus Booger, a fucking lame and cringe way to kill off King Nixel if you ask me. Also can I just say that the whole premise of the I-Cubits is just such a boomer plot? Like apparently the I-Cubits are supposed to be an allegory/commentary on Apple products, so yeah the whole moral of the story is "Phone = Bad". Ok boomer.
In conclusion I agree with Anon, Mixels peaked with M3 and everything else was just downhill from there.