A number of things going on here that's different between #Rotor (pin-fin) and Cascade.
First and foremost there's the issue of the base-plate thickness. The Cascade uses a very thin base-plate, but is able to get away with doing so due to the honey-comb nature of the cup pattern. The ensures that the base-plate will not flex under normal circumstances. A pin-fin by nature needs a thicker base-plate as there's no inter-wall bracing between the pins.
A thicker base-plate means a greater cost in terms of a thermal gradient through the copper, but is also offset by better thermal spread through the copper.
Where it gets interesting is as the jetting is introduced, the impingement efficacy of the jets is such that the heat doesn't need to spread as far before it gets soaked up effectively by the water. So basically we get left with paying the cost of moving the heat through the thicker copper but reaping none of the rewards for improved heat spread.
This is exactly why thicker base-plates tend to be better at lower flow rates, but we see their cooling performance taper off rapidly at higher flow rates, whereas the thinner base-plate designs just keep on getting better. The challenge here of course is to make a thin base-plate design that performs at least as well as a thick base-plate design at low flow rates.
We also need to look at the flow. A pin-fin block is basically a lateral flow block, meaning the water flows sideways through the pins. This sideways flow interrupts the efficiency of jets and also pushes them sideways. Basically what you end up with is an effect that's not really different to just having a single inlet of water mashing down. The Cascade with its injection tubes and cups ensures that each jet region does its job effectively and independently of any other jet, and that the outwash doesn't turn the lot in a just single big mash water flowing down. The Cascade is an array of in-out injection points, with no injection point interfering with any other one.
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