What you are describing is how abatement works but the reason for the abatement was that the new pensionable job was by virtue of the previous military service (ie. it was not subject to 'fair and open competition').
Regardless of whether you rejoin as CS, FTRS, ADC or whatever else commitment / contract, the whole notion of having pay or pension abated is frankly grossly unfair and is why I, and many I know, will never work for any organisation that operates such a practice.
If on leaving the military you get another job, which you have to apply for, then frankly it's none of their business whether you have a second income or how you got that income stream. And frankly, saying you are only eligible for the job by virtue of your previous experience, that is little short of bare faced cheek.
I can't think of any other organisation that would penalise you for your previous experience, which THEY wanted to use and benefit from. If anything, previous experience should attract a premium to your salary in recognition of the fact that they are getting a finished product and don't have to invest in large amounts of training and development time.