I'm not going to make excuses, but it makes sense that they offer a round grip and a few others. Offering "every grip under the sun" would be a stock nightmare, particularly when you can change the grip yourself so easily.
The stock grip is round because it doesn't require you to put it on within half a degree of accurate. A grip that's off by a few degrees can throw off your aim, nullifying all the effort you put into finding a putter you can aim.
First, the grip is an issue. I am surprised that a company selling $400 putters don't offer every grip under the sun. I was using and have been using the same Golf Pride "Special" grip for the last 6+ years. After playing one round with Edel's grip, I have since changed it twice. Unfortunately, Golf Pride no longer makes the grip I've been using, so I am now using a Winn. It's not bad, but the angles are taking some getting used to. Plus, the softer grip may be affecting my feel.
It could certainly be contributing to your poor touch.
You also changed the balance and weight of your putter if your fitter didn't account for (or you didn't after the fact) the grip you were going to use. The bigger grips weigh more.
Next, the vibration (or feel) and sound at impact are different for me. My previous Never Compromise gave a different sensation and sound - more of a medium-pitch, pong noise. By contrast, my Edel has a solid whack feel and thud noise. My distance control is fine, but the sound and feedback I receive makes me think mishit. Thus, I believe this is translating into a lack of confidence in the putter. It's not with all strikes, but with most.
For all we know you're hitting the ball off the toe or heel. Maybe you actually ARE mishitting it.
I am planning a trip back to my fitter to re-evaluate the putter setup. I think there may not be enough loft. The thud I mentioned above may be because I'm striking the upper half/ridge line of the putter face. The metal of these putter is so soft it leaves marks. I have a lot of stike marks across the top part of the putter face and less in the center. There have been strikes where things feel supper sweet. I suppose those were the center hits. Either my forward press and stroke are the culprit or not enough loft.
The metal probably isn't being marked up from hitting golf balls… Are you sure it's not from putting the club back in your bag or something?