I think the math is a little off.
So 6 crits total plus the focus token for flipping cards.
Decimator has 4 shields 12 hull. You roll 3 crits then 3 crits again.
the first attack and the first crti are against the shields. 2 crits left.
Major explosion rolls a hit and flips a direct hit (3 damage) the last one rolls another major explosion and flips up another direct hit (3 damage) Rexlar uses his focus token to flip up one of the major explosions which give another direct hit.
So there is 2 face down major explosions and 3 direct hits which comes up to 8 hull damage. Major explosion is a buff to minor explosion but remember only 7 of the cards are direct hits and a lot of the critical hits are not lasting effects. Yess there is a possibility of getting 3 hits now (so now Soontir can die in a single crit) but honestly aside for direct hits the damage deck has lost alot of its lasting effects.
Lore has it right. In this particular scenario, Rex uses Opportunist to add an extra attack die. You also only accounted for one of the Major Explosions getting flipped back up, but Rex's ability causes all facedown cards to be flipped up, including crits that had already been flipped facedown.
And I'm good with the new damage deck. There aren't as many lasting effects, but the new crits are almost all terrible to receive and painful as long as they last. The old deck was brutal against things like named HWKs (Injured Pilot, Munitions Failure and Minor Hull Breach really hurt here) and trivial against things generic TIE Fighters.