Players action economy will be a fraction of what it was in all past editions.
I fail to see how.
Anyway. Let's look at 3 players.
A: X+1d6: Rolls 12
B: Y+3d6: Rolls 26
C: Z+4d6: Rolls 31
SR5:
IP1: C acts. B acts. A acts.
IP2: C acts. B acts. A acts. (Assuming A didn't take a -2 penalty by now.)
IP3: C acts. B acts.
IP4: C acts.
Reroll. C got 4 attacks, B 3, A 2. That's assuming the fight lasts this long.
SR6:
CT1: C has 1M, 5m, can trade to have 2M, 1m and attack 2x. B can trade all Minors, or keep them for stuff. A cannot trade.
CT2: C has 1M, 5m, can trade to have 2M, 1m and attack 2x. B can trade all Minors, or keep them for stuff. A cannot trade.
<repeat ad infinitum>
C got 4 attacks, B 2~4 (depending on if B needs a Minor for something), A 2. Let's assume B took Cover once, so scores 1 attack in CT1, then 2 in CT2. Then in the end both still have the same amount of attacks as in SR5.