To break with one of the classic alternate history cliches lets not assume that Brussilov gets killed ITTL. He just ends up on the wrong side of Russian army politics early in his career and never manages to rise through the ranks. IOTL he gained a lot of positive attention in the Russo-Turkish War of 1877-1878. ITTL that doesn't happen.
WW1 still happens like OTL but Brussilov participates as a low ranking general and has no opportunity to distinguish himself. He is a pencil pusher or has an unimportant command.
WW1 until after the failure of the Lake Naroch Offensive happens by and large like OTL (butterfly net!).
However after the Lake Naroch debacle butterflies start to flap their wings.
Classical Generals still using the old tactics are in charge of all fronts and there is no influential figure championing the use of "Brussilov-tactics".