I have to disagree. I don't think it was a mistake at all because, in the grand scheme of things, Axel is doing a solid job as a heel champion in my opinion. He hasn't been blowing the roof off the place with how good he is or anything of that nature, but he's ultimately done a good job with what he's been handed by WWE creative. Can't really ask or expect more than that from anybody.
It does seem as though Axel was rushed into the IC title picture. It seemed pretty obvious, at least to me, that WWE's initial plan was for Fandango to win the IC title because he was originally scheduled to face Barrett & Miz. However, as sometimes happens, things happen that disrupt plans. With Fandango out due to a concussion, WWE did what was, in my estimation, the best thing they could do: they put somebody completely fresh in the title picture. In recent years, there were tons of complaints in regards to WWE not elevating anyone fresh into a push or title run but now that it's becoming a more common practice, Axel's a mistake?
As far as facing off against guys like Cena, Orton, Punk and the likes; do you want the IC champ jobbing out to main eventers left and right? I know I certainly don't because, frankly, that's most of what we saw Wade Barrett doing during WrestleMania season. Mid-card champions are, generally speaking, supposed to wrestle against mid-card competitors. Guys like Cena, Punk, Orton, Del Rio aren't mid-carders. They're higher up on the totem pole and, as a result, it's not usual practice for the mid-card champions to go up against them. Often times, when they do, they wind up losing. When that happens, then you have internet fans & dirtsheet writers alike bitching about the mid-card titles being devalued by having the mid-card champs job out to wrestlers higher up on the card. Guys like Sin Cara, Barrett, Miz, Kofi Kingston are frequent mid-carders, hence they're guys that Axel should go up against on a regular basis.
RVD only recently arrived in WWE and I won't be at all surprised if he winds up feuding with Axel very soon. Christian is also a logical choice but he might be WHC after SummerSlam. If not, then Christian will probably be right smack in the middle of either the IC or US title pictures. In the grand scheme of things, I just don't see what's to complain about. Axel is doing a solid job as mid-card champion, he's having good matches against mid-card opponents and is being booked as a mid-card champion generally should. If he's not getting the same sort of hype & attention as guys like Cena, Orton, Bryan, Punk & Lesnar; it's because he's not supposed to since he's, and I can't say this enough, a mid-card star at the moment.