I’ve got an Aerus Biospeed bag, which is a soft case and just a tad past the limit on what can get checked without a bike fee. That said, out of four flights, and have only been charged regular checked baggage fees each time. That’s partially down more to trying to be agreeable and nice and making it ‘easier’ to not charge me the higher fee than anything else. No damage to the bike, and a friendly note inside from the TSA every time.
Some friends have the Orucase Ninja Bike case, I believe it legitimately comes in under most airline’s size requirements for regular checked bags. In four trips they also haven’t had any damage to the bike. However, you have to take the fork off to get it down that small.
For both bike cases, the rear derailleur is removed as part of the packing process, and separately protected.