Motion-control shoes have sturdy arches for limiting pronation. These shoes exist because many in the business of sports medicine believe that pronation is bad for you. Others do not. My opinion is that excess pronation requires more movement of the bones and joints of the foot, ankle, knee, and hips, so there is certainly more potential for injury. However, it has been noted that about 6 years ago, the world record for the marathon was held by over-pronator Haile Gebrselassie, so it may not be all that bad.
Since runners of that caliber are the product of many years of training and adjustment, it would probably be unwise to advise someone training for their first half-marathon to toss their motion-control shoes and go natural. Then, there are those who would, mainly because of what you just went through. I'll leave that decision up to you, your coaches, or physician. What we need to figure out, though, is why the blisters are only on your right foot.
If you do a lot of running on the side of a road, your legs and feet have to adjust to the gradient of the road that is pitched away from the center for better drainage. Your body will seek to be perpendicular to the pull of gravity, and the foot on the high side may supinate slightly, while the other foot pronates a little more to match the road surface. I've developed similar injuries after running on such surfaces, so that may be the case here. On the other hand, most people, when measured, show that both legs are not of equal length. This can force a similar scenario, even on level road surfaces.
There are other anatomical conditions and biomechanical traits that can explain why one foot might run into that arch more than the other, including differences in arch height. All of these conditions can be assessed by a Physical Therapist, and many by Podiatrists, MDs, or at experienced running shoe stores. It also helps to have such professionals observe you running on a treadmill to pinpoint differences in form that might lead to the blistering of one arch over the other.
There are many approaches to handling this. Pods & MDs might prescribe an orthotic for your shoes, but these are often very uncomfortable for runners, and may even cause other injuries. Some sports orthotics are very good, but expensive. If you prefer to actually correct the condition, there are exercises for strengthening, even raising a fallen arch.
Some runners just buy a more forgiving shoe to save time, after training in motion control shoes for a while. I started out in that kind of shoe and moved to neutral shoes as I got stronger. Since my feet and arches were not entirely symmetrical, I put an additional pad in one shoe to get around a similar problem. It probably won't hurt any more to experiment a bit, than what you have already experienced.
My advice to you, now that you have run your target race, is to take it easy as you have been doing, research the possible causes as you have been planning, and find a solution before any more serious training, as I'm sure you will. One more thing, is that the average runner will run into a customized set of injuries any time they radically increase their mileage, as you have done. Even if you do nothing special to address the problem, it may gradually go away as you toughen up. Gebrselassie had to run 6 miles to school and 6 miles back when he was a kid, so he toughened up early. Luckily you have more options. Good luck!