Well of course it wasnt unbeatable even at its best, but it was very difficult to beat. Although the weapon was very effective the real problem for most opponants was that it was nearly impossible to get under it at the front, and due to the excellent driving the front was all most other robots ever saw. Tiberius actually has a more powerful weapon and is certainly much better armoured.
A bit like the heavyweight boxer Mike Tyson in an odd sort of way. At his peak everyone was talking about how hard he hit- and he did hit hard- but the reason a lot of the other big guys couldnt cope with him was his defensive movement and speed...
The ACW was quite neat. Razers design made it very effective against most normal robots, but Tornado put the boot on the other foot by working out how to negate Razers advantage. Crushers like Razer are fairly straightforward to design a defense for, but unless you can swap out your ACW for a more conventional configuration your robot is useless against most non-crushers.