Thermal cycling, strictly speaking, has nothing to do with the hardness levels.....it is to reduce aus grain size. However, reducing aus grain size reduces hardenability. This means, at the end, you need a faster quench to get that max hardness. In other words, take Shiro and quench as received, in P50, you'll get, what? 66HRC+. Take Shiro and thermal cycle it a few times, lets be excessive here and thermal cycle 5 times, you will reduce the hardenability of the steel to such an extent that P50 will no longer give max as quenched hardness. So in that sense, yes, thermal cycling does reduce the as quenched hardness...but it is because the "standard" (I hate to use that term here) quench is now too slow to get the job done. To get that back, you need to to quench in water/brine, or....."start over" and normalize it.
I'm not sure about that last statement. What do mean by that? You always want to shoot for max as quenched hardness and then temper for desired HRC. TME should not be an issue with these steels, as there is no reason to temper them that high. These steels are made for high hardness, thin edges. If you are tempering Shiro and Ao in TME range, then you're lowering hardness levels to such an extent you should be using a different steel to begin with. I'll let others chime in....got work to get done.
