I would not niche the Hell Bent as a powder only or a powder specialty ski per se. It is an all-around play/fun ski. One that happens to be powder oriented. Or maybe better described as highly powder capable. But they will absolutely play well on soft groomers too.
There is a school of thought that with this, and other fat rockered skis (eg Pontoon, Kuro, etc.), any of the longer lengths has a ton of "float". So the question is "what are you going to be skiing with it?" If you will be skiing typical groomers, playful powder, chutes, trees, etc. - the "go-to" length is 179. In fact, one of the two best skiers I know is into season 3 of using the 179 for trees, chutes, pillows, etc. - and considers Hell Bents an ideal ski for this kind of terrain (although his POV is likely skewed by the fact that he does all that sort of stuff switch as well) .
For big, open, fast lines, big faces, etc. - - then the 189 might make sense, depending on your size & skiing style, because the extra length offers a bit more platform for stability at speed.
As BWPA noted - the sizing on these is a bit nuts. The 179 is more like a 185 in almost any other ski. Likewise, the 189 is pretty much the same length as most "195" length skis.
Like any other type of ski, you need to "get the hang of them". There are plenty of people skiing them in cutup, on groomers, etc.
(context: My family has all 3 lengths. Between us, we have a couple hundred days (at least) on them. I've skied both the 179 and 189. I'm roughly the OP's size. I'm a pretty average skier. If I were buying a pair today, it'd be the 179. )