Yeah, it's just a simple way to make a part. Instead of fully melting and pouring to a mold you instead dump a powdered form of the metal into it and then use heat and pressure to not fully melt it, but heat it up to where the combined heat and pressure causes the particles to begin fusing. Relatively speaking it's quick, easy, takes less energy and so on. It is quite brittle, however, and not as strong in general since you don't get nice, long grains in the metal.

All other things being equal, yes. It's just a (much) cheaper process for when you don't require the highest possible strength in the finished material.

This is more of a process issue than materials issue. It's made with a sintered powder process, which always results in a relatively brittle end product. Sometimes that's totally fine because you don't need the full strength of a cast or forged part, but obviously that wasn't the case here.

As for the China association that'd be from the cost correlation. You can find sintered parts made all over the world, but seeing as the cost of labor is also low then anytime someone wants the lowest possible total cost they're likely to get a sintered version that's also made in China.

The Naga is actually quite easy to open and clean, and you can also easily replace the switches in them. I would recommend that when opening one for the first time you leave out all the main casing screws except the one in the back of the wrist rest as that one does more than a good enough job of firmly holding it shut. I'm still using a 2014 model to this day and replaced the left button microswitch after 5 years as well as the scroll wheel encoder. It uses standard Omron D2FC-F-K switches and if you have any experience soldering you can do the job in a jiffy. The only difficulty is getting the teflon pads off without damaging them the first time due to the strength of the adhesive, so along with your bag full of switches for $5-10 off ebay you'd also want to spend another $5 on some replacement pads if you go the route of repairing it.

Honestly the only thing I'd ever replace my Naga with is another Naga, because the functionality can't really be beat, only matched. I have a secondary Mamba that I might swap out for a Viper Elite or equivalent at some point, but for the "MMO" style mouse there's really not many options other than the Logitech G600 and Corsair's Scimitar, but that's just replicating functionality you already have, not improving on it. Can't comment on whether their overall quality or handfeel is any better or worse, however, as I haven't personally used them.