I just got my X27 last night too. Couldn’t wait to try it out so I took a 12” round of maple, set it on my splitting stump and let gravity do the rest. I was shocked when absolutely nothing happened.
Well, I don't just set my axe next to the wood and expect it to split on its own, but my experience was very different from yours, under what sounds to be similar circumstances. Attached, please see photos from about a full cord of silver maple that was split between 1 day and 2 weeks after cutting with my brand new X-27.
As the title of this post notes, this was a side-by-side comparison of the 2 Fiskars axes, along with few swings with my 'Monster Maul' (now recently departed via Craig's List). So your wood may be different. But a lot of this wood was 12 - 14" diameter maple, as yours was. If you look at the ends, you can see that this was not all straight grained wood. In fact, I intentionally split a bunch of knarly stuff to try out my brand new X-27.
With the heavier head on the shorter axe I could drop/push it through the smaller stuff (4 to 8" diameter, clear rounds). Because of the longer handle and the smaller, narrower head on the X-27, I had to swing it over my head, similar to your 'Roundhouse' motion, but I only had to lean into it, or apply a lot of force, on the larger rounds, or those with knots, crotches, etc. Otherwise, momentum carried it through.
As I noted, I intentionally cut my rounds shorter (10 - 12"), especially if large diameter or knarly, to make them easier to split. As I also noted, it took a little while to get used to this axe, compared to my 28" Fiskars, which is why I split over half of that cord before trying to form an opinion.
You should do a side-by-side test with your other maul or axe on a bunch of your wood to see what works best for you. You may prefer the maul you are used to, or it may work better for your wood or your splitting style. But I would not call these axes gimmicks. It might just be a preference.
Philbert