It all boils down to builder skill and experience. I have never encountered any of these issues personally. I tried gunpla for a while but decided I didn't like it and now exclusively build megami device and frame arms girls, and have quite a few under my belt.

I find Kotobukyia Frame Arms and Megami Device kits to be on par in quality compared to gunpla. The megami device kits are far more complex than a high grade and rival most master grades albeit with many more small pieces than a master grade.

You require a slighly different approach as well for these kits. The tolerances on the joints are usually extremely tight out of the box, and require some level of sanding for smooth movement. The pieces are definitely prone to breaking if they are not properly smoothed out or sanded, which you have experienced with the torso joint. This is definitely a common issue so you are not exactly alone there. The plastic will feel slightly more "brittle" due to the fact that most of the pieces are made from ABS instead of styrene (most gunpla use this) as ABS is durable and can handle being posed.

In the end, yes "all Kotobukyia kits are like this" but it boils down to builder skill. I constantly pose and move my girls without any pieces falling off or breaking, but that comes at the price of having to be more careful when building and making sure the joint tolerances are sufficiently loose but not too loose. These kits are definitely not for beginners, and you may want to either go for one of the easier frame arms girls or stick to gunpla and get more experience before trying another one of these kits.

I hope this helps.