I'm going to play a bit of devil's advocate here and remind people that this unit isn't really intended to be roadworthy. We are talking about a $180 wireless unit with a maximum 50-foot range and no ability to manually select channels. It is very much designed for the occasional user or light gigging at best. The receiver is plastic even. So saying it isn't roadworthy is kind of missing the point.
Further, I actually think it's great they went with USB for power. Yes, little 9v plugs are standard these days, but a) they weren't always (and there are still many pedals with non-standard plugs) and considering guitar pedals are the only thing using that plug, it's probably not going to stick around forever. With a USB plug, I can be truly wireless, powering the receiver off a standard USB battery pack. Technically this could be done with a Volto if it used a standard 9v plug, but that requires a more expensive specialty battery (that is frankly less road worthy) instead of the cheaper, higher capacity battery pack I already have (I actually have both, but that's not the point).
If the port is breaking after a couple times of use, as you describe, then that is poor design. As others have mentioned, phones have been using these plugs for years with no problems despite near constant use and abuse. If they just have the plug in there sort of floating on its pins, that's not very durable. At the bare minimum I'd want it secured to the housing of the receiver so the jack doesn't move when plugging and unplugging. Hot glue is one option, though a screw would be better. I'd rather it also be flush to the PCB so there is less risk of solder points coming loose. These are all fairly simple fixes that could be easily be changed on their part (or my part, really, but I'd like to not have to). Would also be good, speaking of roadworthiness, to have recessed the jack somewhat so that there is less risk of damaging the jack by bumping the cable.
In conclusion, not disagreeing with your sentiments about it being designed poorly, but I think there are some important caveats. And now that I know about them, I'm tempted to open mine up and reinforce it...