You know the vast periods of downtime you have between Blitz Phases? That is boring as it currently stands. You can literally stand on the opponent's flank for the vast majority of your rotation and you just go through your GCD rotation. You might have TFC randomly come up, but you also might not. Positionals are an easy way to keep you busy during that time. They are also not as punishing as people kept making out either, as an example, you do 3 GCDs, Dragon Kick, Twin Snakes, Snap Punch), all from the flank, but the boss moves at the last hit, so you miss the last one. Currently, you would lose 60 potency for missing it. If that 60 potency was spread over the 3 GCDs, you only lose 20 potency and Dragon Kick > Twin Snakes is not an uncommon combo to have.

I could make a claim that, on average, I suspect you lose less overall potency for having positionals on everything than having positionals on just the 2 GCDs, or at the very least, they are even. There is zero chance that you lose less potency by having just the 2 positional attacks than having them on everything.