It's hard to think of another name that would have fitted the characteristics of the most famous Dreadnought as well and done the same job of defining an entire kind as well as class of ship. The name had been in use since the 16th century, but was perfect for this ship with armour and armament like never seen before. And it's a noun but was not one in common use, so could assume an unambiguous meaning in general parlance.
I hate RN ship names in general as they suck and don't have to. Here we have the world's most ancient navy still in existence, that once ruled the world's seas, centuries of tradition behind it, and now shrunk to a fraction of its size at its peak. You'd think every single name would be full of historic import and redolent of past glories. Instead, they're usually lame and boring. There's an entire Ships' Names and Badges Committee that labours over these choices (or possibly picks with a pin). You could keep the badges side of things, but otherwise sack the lot and give the job to me, I'd do it much better.
Why is an alternate name for Dreadnought required, may I ask? Knowing that would help in picking one to suggest.