You're describing problems that are typical to most larger drum companies. It happens to smaller ones too, but the variation between good & bad is usually greater from company to company.
Through our finishing shop recently, I've seen two examples of shocking quality/workmanship in top of the range lines from a major manufacturer (not Sonor). The quality was so bad, that someone couldn't fail to notice the mistakes/poor materials, yet the product still went out of the door.
Sending out a ply shell that's warped is actually fairly difficult to achieve. The production process for ply shells is so simple, they're normally pretty much bombproof. A solid shell form, I could understand more, but of course, it still shouldn't pass inspection.
As for filler in the bass drum, someone within Sonor has taken the decision that that's acceptable. I understand how things get missed in a volume production environment sometimes, but deliberate decisions allowing sub standard work to go out without customer consultation, is another matter. It take big balls & a real desire not to compromise to scrap potentially expensive shells. Commercial pressures are often high, & a call has to be made in one direction or another. Ultimately, it's how the company responds to faults in workmanship/poor quality materials that really matters. Screwups can happen to anyone, & sometimes external factors degrade a product outside of the manufacturers control, no matter how good their intensions are.
In the industry in General, I'm not aware of any poor quality trend that applies to Sonor more than any other company. I am seeing increasing numbers of examples of poor work from another manufacturer though, & that's very disappointing. I guess companies have cycles & maybe the odd poor quality employee. It happens