RDX & TAPE
With the RDX spec being what it is, then it''s not much more than a ruggedised version of the way that I back my PC up at home (removable USB as you are asking). At 45Mbps per cartridge, it's hardly flying and that's to be measured against LTO5's 140MBps native (realistically 200MBps with compression) and 1.5TB native capacity (about 3TB with typical compressible data).
"Cloud" backup would be fine, apart from the issue of performance. If it is to get anywhere near the performance of even a single USB 2 drive then there it will need network links approaching gigabit speed. Even if inremental backup is acceptable and you can thereby get away with slower speed, heaven help you if you need to do a complete restore.
This is not simply an issue for companies - many people now have local data stores in the region of a TB and upwards (all that camcorder footage has to be stored somewhere). Cloud storage simply isn't up to it at the moment. If your are a big company it's likely you will have anything from tens of TB to several PB of storage to manage.
The greatest advantage of offline disk storage is that it is likely to be less prone to media failures than tapes (although the devices are generally more fragile) and is a good solution for small/medium companies. Who knows, it might replace tape eventually (LTO is showing signs of reaching it's natural limits), but it's still not yet competitive with tape on capacity or cost grounds.