I happen to be in a special situation here. One of my softwares, Redis, has a very permissive license that was used by many vendors to sell it. At the same time, I'm a lot into 3D printing. So I guess this gives me some perspective on both of the sides of the matter, and what I think, TLDR, is: Bambulab effect on the 3D printing ecosystem is going to be very positive. A few considerations:
1. Prusa is blaming the Bambulab OSS situation, but the reality is that they struggle a lot in innovation, recently. I'm a Prusa Mini and MK4 owner, so I'm kinda of a fan of them, but still... They had struggled to move raise the bar, happy enough to innovate very slowly, with their huge delays with the Prusa XL, and exploiting the fact that other companies were just doing terrible copies. Bambulab before anything else saw that from the POV of technology there was too much left on the table.
2. Prusa itself based its work for PrusaSlicer on an existing open source slicer (written by an Italian guy, btw). While they continue to release PrusaSlicer as a free software, as the license requires to do, what they did renaming the software "Prusa Slicer" is a form of ownership appropriation. PrusaSlicer is a great software that can be used with many non-Prusa printers, my point is just that different ethical perspectives may lead to different conclusions. One could argue that Bambulab created their own slicer instead of just contributing to PrusaSlicer because the naming and the setup of the project makes it hard to do so.
3. Bambulab is also being cloned. The fact that their hardware is not open source does not mean people can't copy the design. The general ideas that make Bambulab printers great can't be patented or copyrighted. See the Creality K1... it resembles Bambulab printers a lot.
4. After Bambulab showed the 3D printing community that it was possible to build better printers, the whole 3D printing landscape became immediately much, much better. They raised the bar. Maybe Prusa will struggle and even fail in the next years (that's my prediction: they will fail, but slowly, since the management is too lacking), but the 3D printing world will be overall much better. In just two years, the average 250$ FDM printer jumped from terrible to totally ok, and this is some kind of value that Bambulab provided, regardless of licensing.
5. One thing that is killing Prusa is in some way they don't use OSS software enough! The future is Klipper, but still they continue with their not-invented-here syndrome to develop their Marlin twist.
6. Finally: using open source does not make you ethically required to open source your stuff. Open source licenses have terms: you just need to follow those terms. If you open source stuff, you are great, but failing to do so does not make you terrible. Remember that in the 3D printing ecosystem there isn't any cloud-companies situation like in the SAAS scenario, where there is a monopoly that allows only a few to exploit OSS value.