The is still zero evidence that sitting on something that doesn't feel uncomfortable has any effect on your back. You can sit on a chair without any backrest for years. In fact a lot of chairs for work do not have backrests. Now if you can't find a comfortable position and you're sitting in pain then yeah. But who does that?
I can't tell if you are being sarcastic or not but if you've ever sat in a chair without a back you'd quickly realize that it's not something you can do all day. Your back will get tired and your posture will worsen as the day goes on. This is regardless of whether you have a bad back or even workout your back, shoulder, and core. Keeping any muscle contraction that long is not reasonable. Kneeling chairs are the only acceptable backless chairs for longer periods, although a good number of them do have backs anyways. This is because the spinal alignment with these chairs is different then your regular chairs. Of course these types of chairs are not for everyone either with their own set of pros and cons.
There are dozens of studies showing the benefit of properly designed chairs on the musculoskeletal system as compared to poorly designed chairs.
The level of comfort a chair provides is a completely separate matter from the long term impact a chair will have on your body. A chair can feel comfortable but promote poor posture and provide poor to no support. It is important that the end user finds a chair comfortable but not at the cost of their own health, especially when you can get both in mid-range to high-end office chairs. Consider that Steelcase and Herman miller both design their chairs to be sat in for at least 8 hours every day and conduct dozens of ergonomic studies prior to release. Meanwhile most gaming chairs are designed to look cool first and foremost and are simply reskins of the hundreds of other chairs that are carbon copies.
