you're neglecting the 1.3 modifier we get from Shield Mastery. that bumps up the Lavanthor to 1144 when shield block and modifier and just 572 when no shield block
and the GAB at 673 with sb and trinket up 336 without sb and 152 trinket down but sb up
and passive gab has 76 sbv.
so you'd have
lavanthor:
(1144*10 + 572*10)/120 = 143 sbv
and
GAB:
(673*10 + 336*10 + 76*80 + 152*20)/120 = 185 sbv
GAB/Coin wins.

