It's all economics.
The bottom line is that if they hire a low timer, chances are he will be with the company for a longer period of time, thus effectively decreasing attrition rates and training costs. The low time F/O has a longer time to upgrade to captain, and the captain once logging PIC will have a longer time in the right seat as well, while he logs his coveted turbine PIC.
Airlines are acutely aware that the PIC usually has things well under control 90% of the time. They usually have many hours and plenty of experience with various weather and equipment malfunction scenarios. It is fair to even say that they are more than capable of flying the jet all on their own. Before assuming the position of a captain in an RJ, they have also proved themselves capable of that position and responsibility. The RJ's that are being flown by these captains who are paired up with "low timers" are very user-friendly and made to fly easily, to the point of being flown by themselves. The systems are designed to make the job of piloting almost non-existent. The massive amount of regulations, SOP standardizations, routine routes, etc. make this type of operation fairly safe. These are the odds that these airlines hedge.
To be fair, there aren't as many 500 hr pilots being hired to begin with. Most have a minimum of 1000 hrs. and usually much more along with a decent amount of multi time. The ones that have less TT and ME usually are the ones who come from some sort of structured training outfit and even then, they are usually sharp individuals. If one can make it past an interview, sim ride, training, IOE, etc. successfully, then they have met the minimum qualifications. They then can meet that 10% gap.
Now it is true that they have to be baby-sat to an extent. Every new co-pilot does. Some will be quick learners and others will be require more patience. Every flight they embark on will increase their knowledge and experience incrementally, until they themselves have acquired the aforementioned requisite qualities and characteristics of those that have mentored them over the last few years.
It is fair to say that after a couple of years in the right seat, these low-timers, are no longer that and have become more of an equal in terms of being a crewmember.
Yes, things go wrong on occasion, and maybe there are isolated incidents in where the F/O was not much help or perhaps more of a hindrance, but these occurrences are very rare, and the airlines know this.
Some of you may recall the history of a vehicle called the Ford Pinto. This was an instance where a corporation felt it was more economically feasible to pay out in fatality lawsuits than to recall a vehicle that needed a 10 cent part retrofitted. Back in the 70's when Japanese cars flooded the market, Ford needed to answer this with a low-weight, low-cost version of the popular Toyotas and Hondas. It needed to be a certain price and certain weight. They rushed the design and production of this vehicle into the marketplace, only to realize after the assembly lines had been built that there was a minor flaw. The gas tank sat too close to the bumper and when this car was rear-end in an accident, it would not only trap the occupants, but caused an immediate explosion, burning the victims inside.
Ford knew of this problem, but their actuaries calculated that it would be much cheaper to wait for an accident to occur where someone was charred and might have had the impetus to sue. If they lost, or settled, it would cost them a lot less than to have each vehicle retrofitted for a part costing a mere few cents during a callback.
